Us pagans celebrate Samhain (pronounced sow-en) every year on October 31st. To the majority of us, it is a time to honour the dead. We honour our ancestors, those who died in battles or because of strife and anyone else who we love who has passed into Summerland or beyond.
Most of us have some form of ritual followed by a feast and much merryment!
Yes, we dress up - very like christians do. We also acknowledge that this is the second time of the year when the veil between our level of existance and the otherworld is at it's thinnest. So it is a great time for communication with the dead. 'Journeying' and meditation can be particularly effective around this time! 
In the tradition of the Celtic religions, Samhain acts as their New Year. As the Earth is going into slumber it is time to renew everything. Yourselves, your ambitions, your dreams............ It is often thought of the most important festival of all.
The Sun King is sacrificed back into the Earth at this time and the Goddess (as the crone) mourns him until he is reborn at Winter Solstice (Yule). He travels the underworld gaining strength, courage and wisdom.. Now the dark half the year commences. whilst this is the end of the old year, it is the beginning of the new!
Symbols of Samhain - Pumpkins ( the Human head is the seat of the soul) with a candle in them carved as a head symbolises the light of the soul!
Besom Broom, to sweep away the old, the past, and start anew (and also to get rid of garden leaves etc).
Acorns - the seed of longevity and wisdom.
Colours for Samhain are Black, Orange, Purple
Tools - Cauldron (cosmic container of all life and death)
Black candles (to honour the passage of the ancestors into Summerland)
Tree - Oak
Of course there is so much more varied information about all of the festivals. Maybe I will add more later............
Blessings..