Its simple. Just apply. Follow the on-screen instructions.

They will ask you to put their widget on your blog. Copy and paste it as a widget.

After that, wait for the moderators to approve your blog. After approval, use the marketplace to find more blogs to comment on and drop cards. The more cards you drop, the more entre points you get. The more entre points you get, the more advertising you can do at other people's blogs.

Its a whole different ad network. Here's a review:
http://www.imreportcard.com/services/entrecard/