There is a bit of a difference. Advice is more personal, like what you might give to someone who is having relationship problems. A suggestion is more impersonal, for example what you might give to someone who needs help with a presentation. It's a really subtle difference though, and in most circumstances they're interchangeable. As for when to use advice as singular or plural, "advice" is both singular and plural, so you don't need to worry about it.

suggestion --- common activity

Advice:you should do as I say suggestion:you'd better do as I say

If you really want to use advice, which is a non-count noun, in the singular form, you would have to say "a piece of advice".

In Italy the two wards are the same means, in English the 2 wards have the same mean : http://dizionario.reverso.net/inglese-sinonimi/suggest/forced