Session Variables

I need users to login to my site. so now i have a login page. Users enter their username and pasword and then gets redirected to another page.

Now first:

The address bar at the top changes to the new page. Is there a way that this can be prevented? Because after someone logs in once, and get that address, they can use it as a "shortcut" and get into the site without logging in at a later stage.

And then, once a user is logged in, they can fill in all forms and it would automatically add which user completed the form. Instead of re-entering their name / special code. Sort of like a datestamp but with the login details?