But, However, Although

​But joins two clauses.

It must go before the second clause and has a comma (,) before it.

I don't like Facebook, but I use it to keep in contact with friends.

I like cheese, but the doctor told me not to eat it.

​Although joins two clauses.

It can go at the start of the sentence and a comma separates the clauses.

Although I don't like Facebook, I use it to keep in contact with friends.

Or it can go in the middle, with a comma before it.

I use Facebook to keep in contact with friends, although I don't like it.

​However joins two sentences, and introduces the second sentence.

A full stop (period) goes before it, and a comma goes after it.

I don't like Facebook. However, I use it to keep in contact with friends.