You'll be asked to choose the date and time you want tickets for. After making your choice, you'll be taken to the form itself. Don't forget to look for any extra information, such as clothing that may be discouraged (lots of shows won't let you in if you're wearing clothes with logos all over them, for example). The form will also tell you what time you need to arrive at the studio.
When tapings are full or not currently being held, you can still fill out the form to be notified when new tickets become available.
The address where Don't Forget the Lyrics is recorded is:
CBS Television City in Hollywood
7800 Beverly Blvd.
Hollywood, CA. 90036