If you are in an abusive relationship, please don't use any computer your abuser has access to!
Even if you erase your internet browsing history, the abuser may be able to track it anyway.
It is best to establish a free email account (such as hotmail or gmail) at a friend's house or the library, and use the computer from there.
Also, phone calls you make are stored in your phone. You should call for help only from a phone the abuser doesn't have access to, preferably a public payphone or an unlisted number that doesn't have caller ID.