The Wiccan Calender shows the holidays and celebrations of our witches . These celebrations , called Sabbats, begin with the Witches New year on October 31, Halloween.
The Sabbat normally starts at sundown and goes through to sundown the following day.
This Calender is for the Northern hemisphere. Southern hemisphere Sabbats are reversed as the beginning of our Summer is the beginning of their Winter and so forth.

The 8 Wiccan holidays  - Sabbats
(What MIGHT Wiccans actually DO on these days of special power? I certainly can't tell you what all Wiccans do! I would venture, tho, that most are having a jolly good time: getting together in circle; performing some rituals relating to the intent of the specific holiday; perhaps a bit of positive spell-casting, followed by consumption of lots of good food. The Wiccan belief that anything nasty you do comes back to you three times over would not encourage the performance of negative spells!)

Samhain (31 October),
Halloween, is the New Year, usually viewed as the biggest holiday. It is the last of the 3 harvest feasts, following Lammas (1-2 August) and the Fall Equinox, when crops are gathered. Samhain is the last chance to gather any remaining crops. It is a holiday of feasting, yet a time when one recalls and honors the dead. Samhain feasts might have an empty place at the table where a spirit plate is set.

Older legend points to the sacrificed king, who has been ploughed into the earth so that the next year's crops might be fertile.  At Samhain, the veil between the living and the dead is thought to be at its thinnest, so that one might be able to communicate with the dead. (Christian holidays  got superimposed on many of the Pagan holidays, as early Christianity tried to win converts by placing a Christian holiday atop an existing Pagan one. Christians celebrate All Saints Day 1 November and All Souls Day, 2 November.

Yule: Winter Solstice
(The Wiccan holidays are approximately 45 -46 days apart: 45x 8 = 360, nearly the number of days in a year).  Solstice falls on 21 December, give or take a day.  The ancient Romans and Druids give us the custom of decoration of trees and hanging of mistletoe. The God is reborn. This God is the Sun, its mother being the Goddess.

The light has returned. The Sun starts to wax. To celebrate the Sun's return, a Yule log might be burned. This is a holiday of rebirth, including our own spiritual rebirth. Yule is a time to ponder what personal seeds we want to plant within ourselves so that our own lives will re-seed us into the person that we desire to be.  To paraphrase something that Carolyn Myss once said, if you are seeking a best friend who is (loving, caring, sensitive, intelligent, stimulating, vibrant, etc. etc, etc) then you have to build up in yourself the characteristics  that you seek in the other.

Imbolc/Candlemas 2 Feb.   The Sun Reborn.  Brigid's Day
Wiccans celebrate the renewal of the earth. The Goddess has recovered from childbirth, and her child is young. Whereas the trees and plants looked dead in January, the foliage is now beginning to burst forth if the roots were strong.
  This is a time for germinating ideas, as well as clearing out whatever needs clearing--making room for new things to come. It is a time for making sure that our own roots are strong-meaning the roots of our personal integrity.  Christians celebrate Candlemas, "The Presentation of Our Lord," by blessing candles.  The Christian holiday is also known as the Purification.  Who got purified?  Women were seen as IMpure 40 days after having a baby. Now, Jesus was 40 days old and his mother, Mary, was able to present herself to the temple. She was purified.  She could re-enter society!
  1 Feb. is also the Christian celebration of  Brigid of Ireland. Little is known about her life.  (Christians deny that she "evolved" from a pagan goddess cult).

Ostara/Eostre/Alben Eiler/Vernal or Spring Equinox. Lady's Day 
    21 March (approximately) Spring begins.The Zodiac ushers in Aries.
   This is a time of tremendous life renewal. Day and night are now equally balanced, but the days are moving in the direction of more light (greater clarity!)
   This is a time when we might audit our own lives to check if we also have a healthy balance.  This self-audit might include seeking out areas where we require greater inner clarity, greater self-understanding,For example: What kinds of things motivate us? What makes us feel good? What things make us angry or uneasy? Why???

  In some traditions, the Lord and Lady are young and innocent, amidst all the rebirth around them. They will have their handfasting (marriage) at the holiday of Beltane. (In some pagan traditions Spring Equinox is the time of the sacred union of the God and Goddess. The Goddess conceives.
  25 March is the Christian feast of the Annunciation, in which the angel Gabriel announces to the Virgin Mary that she is to be the mother of God.
(The Virgin subsequently gives birth on 25 December.)

Easter
  Easter, the resurrection of Jesus, is interlinked to the Wiccan/Pagan holiday.
  Easter falls on the first Sunday after the first full moon of the Spring Equinox.
  The word "Easter" is similar to "Ostara," "Eostre." To drive in the message of fertility, we have derivative words: estrogen; being in ovary, ova/egg. 

  "Estrus" is the condition for animals that are reproduction-ready, well-known to owners of unspayed cats. Egg and rabbit are fertility symbols. The world is ablaze with life; plants pop up; many animals conceive or give birth. 
  30 April, 1  May; Walpurgisnacht.  Beltaine.("Tene" means fire). The Celts counted days from sunset to sunset, so the dates do not totally line up with our calendar. Beltaine is a festive holiday. It is considered by some as the 2nd-most important Wiccan holiday, taking back seat only to Samhein.
   It is a time of flowers, fires, food, drink, dancing and general merry-making.
   Why the celebration?  Because the Lord and Lady unite in a hand-fasting (a marriage ceremony). The Druids lit fires in the hills to bring the light of the Sun down to the earth. People dance around the maypole, a symbol of male fertility. The cauldron is a symbol of female fertility. Just as Samhein allows for easier access to the dead, the night of 30 April-1 May is the time to view faeries.

Summer Solstice, 21-23 June, Litha,  Midsummer.Alban Heruin. 

   The Wheel keeps turning, and now everything is at its peak. The Lord and Lady are at their personal peaks.  This is the day of longest daylight (and shortest shadows).
  The triumphant sun shines high overhead. Dusk seems never-ending. Although there is not yet a harvest, the seeds are growing. Summer solstice is a good time to commune with the fairies and sprites. Long outdoor rituals could be comfortably performed, since summer has arrived.

  Yet, there is a certain melancholy because, from this day forth, the days will get shorter. The summer solstice, in our life cycle, represents the time of maturity, adulthood, and full growth and power. This could be a time when we survey whether we have strived to reach our full potential; what further work we have to do; whether we are "stuck" as a result of some residue from our childhood that is keeping us from reaching full maturity. Some of us have encountered great trauma in childhood-abuse; severe parental neglect or rejection. We can't just repress these things. But other persons might let themselves be snagged up by a much lesser grievance, real or imagined. Summer solstice might just be the time to say okay, I'm 40 years old, my mother has been dead 20 years, I know she liked my brother better than she liked me, and that's all right because I value mself.
  June 24 is the feast of John the Baptist. The holiday was once called "St. John's Eve."

 Lammas, Lughnassad-   1-2 August.
 Lammas is the first of the 3 harvest feasts. The Goddess is waxing with the pregnancy of the new God, who will be reborn on Yule. The energies of the old God begin to wane. Lammas (loaf mass) was an old English festival for baking bread.

  Maban, Autumn Equinox Alban Elfed. 20-23 September.
  This is the 2nd harvest festival.  The crops are at their peak. Apple cider pumpkins and chestnuts make an appearance. Day and night are again equal. Appropriately the astrological designation is Libra, the scales of justice, equality. This is the time when farmers would get their crops weighed at the marketplace.
  This is one more time for us to weigh our own strengths and weaknesses; to formulate an action plan to accentuate the former and decrease the latter.

  But now the days slide into increasing darkness. This move toward the darkness, the lengthening shadows, foretells the preparation of the old God to meet his death on Samhein. He will metaphorically die and be plowed under the fields, a sacrifice to assure fertility of next year's harvest.
    So the wheel turns.