What types of spells do you mean?
Samhain and Halloween/All Hallows' Eve are different! Samhain is traditionally a Gaelic harvest festival- but eventually became associated with Halloween.
The festival of Samhain marked the end of the harvest, known as the 'lighter half', and the beginning of the 'darker half'. Bonfires were used on this date as a cleansing ritual, and people would often walk through two bonfires in order to cleanse theirselves. Its celebrated as a religious festival by a lot of neopagans ^.^. Its often called the 'Festival of the Dead.' On Samhain, some neopagans, if memory serves me right, have rituals to honor the dead and the deities in their cult/religion associated with them.
Samhain/Halloween is when the veil between the realms are at the thinnest.
People carve faces in pumpkins on Halloween to ward away evil spirits.