In British English, practice is a noun or adjective, and practise is a verb. For example, we would say that a doctor with a private practice, practises privately. There is no such distinction in American English, where practice is both a noun and a verb, and practise is not used at all.
My doctor’s practice is in Sydney. (noun)
I hit a practice shot at the golf course. (adjective)
I must practise the piano more. (verb)