How should I take care of a burn to one of my butt cheeks? I accidentally sat down on a torch.

Ouch! You need to have the area looked at by a wound care physician or burn specialist. Seek help immediately.
Ouch! Keep the area clean by washing with a gentle soap. Then apply antibiotic or silvadene (silver sulfadiazine) (prescription) cream to the area twice daily and cover with gauze and a bandage/tape.
Wound honey. If you can buy get medihoney to area cover with advanced healing dsg by johnson and johnson. If it is tough to cover the area just use medihoney three times a day. Orally take methionine 500mg twice daily until tissue heals.