"Friend's" can also be an abbreviation of "friend is". It depends on the context of the word within a sentence as to how you translate it. For example: "My friend's German but he speaks English really well." - abbreviation. "I always like going to my friend's house - his mum always gives me food!" - possession.

Friends' is the possessive form for more than one friend, friend's is the possessive form for just one friend. Example: "All my friends' parents let them go to town on their own, but mine won't let me go without an adult present." (Plural) "My friend's dog is really cute!" (Singular)

They are both possessive forms. Friends' = many friends; friend's = one friend.

friends is plural from friend, while friend's is abbreviation from friend has it mean that he/she is belong to you or you could say best friend..