Practise and practise are often used incorrectly in written English. Native speakers often confuse the two different spellings of this words, but the difference is quite simple. Let's take a look.

American English

In American English, practice is always spellt with a c. Regardless of whether it is a verb or a noun.

Tessa has softball practice on Tuesdays and Thursdays. (noun)
If you want to inmrpove, you have to practice every day. (verb)

British English

In British English, practice is spelt with a c when it is a noun.

Tessa has two practices a week. (noun)

When practise is a verb, it is spelt with s.

They are very good because they practise every day. (verb)