A tag is something that you stick onto the end of something as a bit extra. A tag question is a small question that you put onto the end of a statement to check that what you have said is correct.
Your statement by itself shows that you mean what you say. For example: It is raining outside. You are telling everyone that it is raining outside because that is a fact. But, add a tag question at the end and what you are saying changes. It is raining outside, isn't it? Now you are checking with the person listening to see if they agree with you.
Tag questions are used all the time in everyday conversation so it is important that you understand how to use them if you want your conversation to sound natural.
You have to put the right tag at the end of your statement, otherwise you will be talking nonsense. For example: It is raining outside, doesn't he? is very, very wrong.
There are three main groups of tag question. Study them, learn which one is used when and your conversation will sound natural and clear.
Group 1
aren't I / aren't you / isn't he / aren't we / aren't they?