The Pagan year is celebrated in a circle, starting with birth, then growth, and in the end death and back to birth once you've come full circle. Specific dates of each holiday are different in the northern and southern hemispheres and may differ a few days from year to year. Consulting a wiccan/pagan almanac each year is a good idea to know the specific dates for the Sabbats.
This site will give you the basic dates for each holiday, what they represent, and some ideas on how to celebrate each one (celebrating each holiday is different for everyone).
Yule/Winter Solstice
Imbolc
Ostara/Spring Equinox
Beltane
Midsummer/Summer Solstice
Lughnasadh
Mabon/Autumn Equinox
Samhain
