To sign up to its instant and only takes a couple of steps.
First you must already have a Enjin account if not, sign up here.
Then head to this link to instantly join the Enjin Affiliate program.
You will be granted with a page that looks something similar to this
*NOTE* Make sure your paypal is the same as the email you signed up with, If not untick the "My PayPal email address is the same as my Enjin account email address" and input your email.
After that simply press the instantly join button and your now setup and good to go!