The website url is www.gsa.gov . On their home page you will see a list of arrows down the left hand side. The second arrow points to "GSA Contracts and Schedules." It is under this heading that you will find "Schedules e-library." Click on the link to take you to the "Schedules e-library."
On this page, you will see a graphic on the right hand side that is a screen shot of the Schedules e-library site. Don't ask me why it takes this many steps to get there from the GSA home page. You'll learn not to ask silly questions like that once you really get started on your GSA schedule.
Now, once you are on this page, you will see a search box just below the welcome message near the top of the page. This is where you will type in your product name or a description of your product. In my case, I wanted to sell polypropylene underwear.
After running the search, schedule 84 returned by the search engine. Sometimes, the search engine will return more than one schedule. If you cannot decide which schedule to choose, you can click on one of the schedules. At the top of the schedule page, you will find the contact information for the contracting officer for that particular schedule.
You can then call or email them with the description of your product and they will help you select the right schedule. When I did mine, I found that emailing my contracting officer was the most effective way to reach her. I rarely got a response or a call back over the phone. But that was just my experience with my contracting officer.
Now that you know what schedule you product will fall under, you will need to download the contract information to fill out.