Basically you have three feilds. You can have more
id || username || password
id will be auto increase and our primary key.
From there you'll need a registration script. Which should check your username and password arent empty you may feel that the person will need to type the password again. As like a confirmation so you'll need to check they match up.
Some people have like username 4-8characters so you can try and use that to if you wish.
Basically once users are inserted into the database you'll need to have a login script. Im assuming you know about md5() i should have said you should use that to encrypt passwords when registering.
Anyways if you use that you'll need that on the login script.
the query should look something similar to this.
mysql_query("SELECT username,password FROM users WHERE username='$username' AND password='$password' LIMIT 1");
then check to see if theres 1row if so there logged in otherwise tell them to try again or redirect them to the login page.
Hope that helps
