It's easy to join up. First you must register using the eQSL Advertiser Registration Page. When your registration is complete, eQSL will send you an email containing your ReferralID number. You then visit the eQSL Link Exchange Program page and choose how you are going to refer visitors to their site. You can either display a banner ad - there are several to choose from in various sizes - or show a little form like this, allowing people to check how many eQSLs are waiting for them.
It's a great way to help publicize a great service and at the same time attract some visitors to your blog or site.