Session variables php

I am new to developing/designing/programming a web site. So far I have put together a create account page, the login page and the page that has restricted access. In mysql, I have a table that has keeps user info and their settings. I am not sure how to setup the user page so that only their row in the table is accessible to them only and no other users. I don’t want to have a separate table for every member. I was thinking that I can set up a session variable that contains their Id # and their user name, and if at all possible, their IP address upon login.

I am entirely new to this, I have been doing as much as I can muster with php. I am using Dreamweaver CS3.

On which page would I start the session variables?
How do I save their username upon successful login as a session variable?
How do I take their Id# from the database and save it as either a cookie or session variable for further confirmation?
Should I even bother with the Id# since the username will be unique? (the Id# is the primary key at auto_increment).
How do I take their IP address and use that as a session variable?
Once I have session variables, can I use that to give them access to their row only by filtering the data, or do I need to do something else?