Advice /ədˈvɑɪs/ is a noun and means a suggestion about what someone should do. It is uncountable:

Let me give you some advice: stay away from Margaret.

Not: Let me give you an advice

She gave him a lot of advice, but I don’t think he listened.

Not: …a lot of advices …

If we want to use advice in a countable way, then we use the phrase a piece of advice:

I have two pieces of advice for you about the holiday.

We use the verb advise /ədˈvɑɪz/ to mean ‘to give someone advice’:

I strongly advise you to lose weight.

They finally did what we advised.