If there is puss, it's infected. Wash it thoroughly. Then apply a topical antibiotic, such as Neosporin, and cover with a bandage. Follow the package instructions on the ointment you choose, to know how frequently to reapply.
Beware of red streaks emerging on the skin around the cut. That means the infection is spreading, and you may need more aggressive treatment from a doctor. If you experience swelling in your glands - lymph nodes, seek help. That means the infection has entered the bloodstream.
