Don't forget to read "safety online" (top right hand corner) for some more online safety tips.
Just to confirm - anything you post on someone's profile is private, but can be seen by another user that visits that page. If you send them a message, then it can only be seen by you and the person to whom you are sending a message.
If you post a comment on the forum, it can be picked up by google for their google search. (This is the same with any forum.) Once it is picked up, even if we delete your comment, some of it may still appear in their search, but they cannot come back and see the whole thing.
But - we do check the site on a very regular basis, and you may notice that sometimes we change or delete forum messages. If I (or a moderator) see(s) a message that I do not think you would want "public," I will change the wording and let you know.
In general - we discourage users from using their real names as their user names. I do not believe that you need to worry about using your school name, as there are many people at each school, and there are many schools that have similar names all over the world. Also, we watch who signs up, so that you should not need to ever worry.