Lots of people get confused over these two but this is fairly simple. Advice, with the -ice, is the noun. It is the recommendation, counsel or opinion that someone offers you to help you make a good decision or to decide on a course of action.
Advise, with the -ise, is the verb. The person giving you the opinion is advising you.
In general, -ise is usually the verb while -ice is the noun. For example, devise (-ise) would be the verb meaning to forming a plan or build something. Device (-ice) is a noun that would be a gadget or object.