There you can read all about procedures and conditions, and apply for participation. They will review your site and send you your Amazon Associate ID within a short time if you are accepted.
As far as we can say, any well-behaving, remotely useful site gets accepted. If you plan to link to Snap-Scan you should mention this site in your application. If you don't have a suitable site, e.g. because you operate with email newsletters, or because you plan to link from an intranet site, you can list Snap-Scan as "your" site and explain the issue.