“Friends” is the plural for “friend”. “Friend’s” is the possessive form of “friend”. Friends’ is the possessive form of “friends”.
Friends, friend’s and friends’ are all pronounced the same way.
We use friends when we want to make the word “friend” plural.
So it is:
I have one friend.
I have two friends.
Friend’s is the possessive form of “friend”. We use the possessive form of “friend” when we want to show that a friend owns something.
This is my friend’s house.
We need to look after our friend’s plant.
Remember we are talking about only one friend. You can replace friend’s with a name if that makes it easier to understand.
This is John’s house.
We need to look after John’s plant.
Friends’ is the possessive form of friends. When the noun already ends in “s” and we want to make the word possessive, we need to put the apostrophe after the “s”.
This is our friends’ house.
In this case, many of our friends live in the house and they own the house together.
In spoken English, it can be difficult to know whether you are talking about one friend or many friends in the possessive because friend’s and friends’ sound exactly the same.
Best friends or best friend’s
Both best friends and best friend’s could be correct depending on the context.
We use “best friends” when you are describing the relationship
We are best friends.
We need to use the plural of friend because there are two people involved.
We use “best friend’s” when you are describing things that your best friend owns(literally or figuratively).
Tomorrow is my best friend’s wedding.
My best friend’s birthday is on Thursday.