Pagans revere the cycles of Nature through rituals or ceremonies of various kinds. Pagans of the western traditions celebrate up to eight festivals or Sabbats each year (not all Pagans celebrate all the Sabbats). They comprise the four solar quarters i.e. the two solstices (longest and shortest days) and the two equinoxes (day and night are the same length) plus four Celtic 'fire' festivals. All these mark important events in the cycle of life and also symbolise changes in the Goddess and God. They are:
Samhain(pronounced "sowain"), 31st October: the feast of the dead; remembrance of ancestors and people, now dead, who were important to us. It marks the end of the Celtic year and the start of the spiritual new year. Also known as All Hallows day, the night before being All Hallows Eve (Halloween) or all souls night.
Yule, the winter solstice, 21st December approx.: rebirth of the sun and the gradual lengthening of the days towards springtime and new life.
Imbolc or Bride's day: start of spring and the return of the Goddess to the land.
Ostara (Easter), the spring equinox, 21st March: Return of the sun from the south, springtime proper. Some celebrate a holy union between God and Goddess.
Beltane (starting on May day): Summertime begins celebrating new life and the holy marriage of God and Goddess.
Midsomer (Midsummer) or Litha, the summer solstice, 21st June approx.: Everything is green thanks to the God of nature, the Green Man.
Lughnasadh or Lammas end of August: the festival of the first (corn) harvest.
Mabon, the Autumn equinox, 21st September approx.: second (fruit) harvest celebration, making plans for the winter months to come.
And finally back to Samhain and another turn of the wheel of the year. or wheel of life

Samhain, Imbolc, Beltane and Lammas are known as fire festivals. Traditionally there was always a fire at these celebrations. These festivals were never held on exact dates for example Lammas would have been celebrated when the barleycorn was harvested. This wheel is sometimes called the Gardnerian Wheel because it is a combination of two ancient wheels (acknowledgements to Kenny Klein). The hunting wheel, the oldest, has two God births: The Oak King is born at midsummer and rules through to Yule when he dies and the Holly King is born. The agricultural wheel has the young God born at Ostara, symbolic of the sun/son rising in the East. He dies in the second harvest, Mabon.

In the different traditions these holidays (holy days) may have different names, for example Imbolc is called the festival of light in the northern tradition.

Western Pagans have no fixed temples in which to worship but instead (usually) make a circle around themselves (or form themselves into a circle) in a room or in a clearing or on a beach or find a naturally ocurring circle such as a grove or use one of the ancient stone circles. Pagans have no hierarchy like the established religions so Pagans are free to follow whatever spiritual path they choose.

Pagans like to celebrate more rites of passage than the prevailing culture. Most people see two rites of passage: coming of age (18 or 21) and marriage. Christians also get a first one, the Christening, though the subject is unable to experience it. The Pagan equivalent of a Christening is a Naming ceremony. Other rites of passage may include Child - celebrating change from baby to child, Puberty and so on. Marriage is called hand-fasting and this may be arranged for eternity or just for a year-and-a-day, renewable. The latter is a great stabiliser against casual relationships and divorces, providing some level of commitment yet recognising that some relationships will not last.