The word practise is a variant spelling for the verb practice. American English spells both the noun and verb forms practice. For the Brits, the noun form is still spelled practice, but the verb is practise.
To practise is to do something repeatedly or habitually. If you've always practised good spending habits, you are probably in good shape financially even though the economy is bad. To practise also means to learn something or become proficient at it by rehearsing or performing regularly. If you ask a Brit how to get to Carnegie Hall, he might respond, "Practise, practise, practise."