The relationship between Samhain and Wicca can be varied since not everyone practices the precisely identical form of Wicca. Most Wiccans do follow the 8 Sabbats of the year, even though these holidays have a specifically Celtic origin. So many Wiccans who follow different pantheons may change how they celebrate Samhain, but generally, the holiday is a big one no matter the details.
So what is Samhain to Wiccans? The holiday represents the last of 3 harvest festivals (the first two are Lammas and Mabon), and a time to celebrate the upcoming dark time of the year.
The dark of winter is typically associated with death and a time to rest and reflect on the past. This usually is connected to honoring our ancestors and communicating with the dead. Different traditions use different techniques, but Tarot and seances are common with most Wiccans.
Considering this to be the “witch’s new year” is a bit of a misconception though some people do view the Wheel of the Year as beginning/ending at this time. Since most Wiccans do see life as a seasonal cycle that never really ends or begins, not everyone marks any set date as the “new year”.
At Samhain, Wiccan covens almost certainly gather for rituals, spellwork or even just to celebrate and honor the year. The specific types of rituals will vary by tradition, but usually include references to the dead, the harvest, ancestors or the dark side of the year.
One bit of a sore spot at Samhain for Wiccans, is the way that witches are portrayed as a costume. It can be a little offense for someone who identifies as a Wiccan or witch to see all the tired stereotypes of pointy black hats, warty noses and general evilness. Then again, some people just take it all in fun and accept that these stereotypes exist and are more of a reflection of witches in movies than “real life” witches.
So for this upcoming Samhain, Wiccans and witches alike will be celebrating in their own way, and getting ready for the quiet of winter. Don’t worry, it won’t be long before the sun returns at Yule and things start to get a little brighter.