Practice - practise

A practice is a noun – something that you do, e.g. “there is a football practice tonight”; “I did 5 hours piano practice yesterday”; “my usual practice is to warm up for five minutes first”; “she is in General Practice”. (If you can say “a practice” in your sentence, then it is practice.)

To practise is a verb – to do something, e.g. “I practised my vocabulary last night”; “he practised his speech in front of a mirror.”