You probably learned that the French word for “friend” is ami. In my opinion, this word is quite strong (except when talking about “Facebook friends”) and I wouldn’t use it as often as the English word “friend”.
Instead you are likely to hear words such as copain (feminine: copine), which is more colloquial and less strong.
J’ai aidé un copain à déménager hier.
I helped a friend move out yesterday.
Ma sœur a ramené ses copines à la maison.
My sister brought her girlfriends home.
Note that the expressions petit copain and petite copine don’t mean “little friend”, but “boyfriend” and “girlfriend”. And when you hear people saying ma copine ou mon copain, they are usually referring to their girlfriend or boyfriend.
Another very common word is pote (masculine or feminine). It is especially popular among young people and it is less strong than ami or copain. You can use it to refer to people who are not close friends.
J’ai traîné avec des potes hier soir.
I hung out with my mates yesterday.
Pote is actually short for un poteau (“post”, “pole”), which is a little old-fashioned in the meaning of “buddy”. Today you will rather hear its verlan version, tepo.
Listen to the examples: