Answer:
Wicca is a nature based religion. So many of the traditional Wiccan 'ceremonies' take place on the solstices and equinox'. A few commonly known ones are
Yule: The celebration of midwinter or the beginning of the sun staying longer in the sky. Takes place during the winter solstice. Common practices include decorating an evergreen tree and burning a Yule log. Similar in tradition to the common American holiday of Christmas.
Ostara: The celebration of spring, warmer weather, and birth- new life. Takes place during the spring equinox. Common practices include decorating eggs (as a tribute to birth) and honoring rabbits (as a tribute to fertility). Similar in traditions to the common American holiday of Easter.
Samhain: The celebration of fall, death, and honoring ancestors. Takes place during the autumn equionox. Common practices include placing candles in hollowed pumpkins to light the ancestors' way home and giving gifts. Similar in traditions to the common American holiday of Halloween (many pagans also call it "Hallow's Eve".)
There are many more Wiccan ceremonies that take place throughout the year. And many are closely related to common holidays already practiced. These three are probably the most commonly known.