I have received an email telling me that someone wants to follow me. I said OK. My question is what can a follower do. When you hear of celebrities getting abuse on their twitter page (I think it is called a time line) I wouldn't like that. I he is following me then are all the people following him also following me?
No his/her follow aren't following you automatically but there is a high probability that they can reach you as well including your tweets. More followers means more audience can have an access to your tweets.
I wouldn't worry about it if someone follows you, the whole point of Twitter is to have followers so that your tweets will get noticed and even possibly retweeted and will reach a wider audience. You do have the ability to follow them back if you wish which I do with a lot of people that follow me. If you do find that you receive any kind of abuse you can report it and it will be dealt with but I would not worry too much about people who follow you.
No, the people following him are not following you. People following you just see your tweets in their news feed and they might react to your tweets also. People you follow show up in your news feed.
If you don't have followers on your twitter account, you tweet status won't reach the people. If he/she is following you, it doesn't mean that all his/her followers will follow you as well. All followers can do is to like and retweet your post.
Infact its a simple logic and I am sure the followers following, the one you follow dont have any access or visibility of your posts. Its always being good to have more followers, however you will have more followers only if you are popular or a celebrity or your posts are interesting. This is the reason, its always good to follow more people first, so your tweets would get more visibility and eventually have more followers.