Is there a difference in meaning between mutlu and memnun?

mutlu : happy
memnun : pleased

and kutlu ?

when do we use each ?

is one formal and other between friends or something like that ?

Mutlu and memnun are pretty much like their English translations that I have suggested.

So we say "çok mutluyum" (I'm very happy) or "mutlu musun?" (Are you happy?).

"Memnum oldum" (I'm pleased) is the shorter version of "Tanıştığımıza memnun oldum" (I'm pleased to meet you) and is used as ("memnun oldum" is used as ) "how do you do".

"memnun" has the main translation of "pleased". It's second trandlations would be "satisfied".

"mutlu" means happy.

"Kutlu" has nothing to do with either of them.
kutlu: 1. blessed
2. "the one that is to be celebrated"

"Bayramınız kutlu olsun" > May your bairam be blessed.

Or the most common usage of the word: Dogum gunun kutlu olsun! Which basically means "Happy Birthday"

Erem,

Oh, now I see where Canlı had the idea of kutlu. The literal translation is "My your birthday be blessed.".