In many English speaking countries (Canada, the UK, Ireland, Australia, South Africa) "practise" is a verb (an action), and "practice" is a noun (person, place or thing). However, in the U.S. of A. "practice" is most often used as both a verb, and a noun, which is why when you write"practise" it often pops up in spell check.
An example of the verb practise:
Don't forget to practise your instrument!
An example of practice:
I have to go to soccer practice after school.
All that being said, if you're in doubt of practise vs. practice, choose practice. Hopefully that's been of some help to you. So if you're Canadian (or from the UK, Irish, South African, or Australian) use your "practise" proudly, but if you're American then you can just ignore this. Anyways, have a nice evening!