You can apply to become an affiliate by clicking on the "Affiliation" menu in the account section.
It would take a few days/hours for you to be approved.
After approval you will see your referal url which looks like this "http://market.internetstones.com/?src=link&ref=yfiyo1XuZD7cL5Lw" on your affiliate dashboard. You can use this link in newsletters, websites etc.
Once you are approved you would be able to access the affiliation menu as shown in the screenshots below: