Clickbank is one of the easiest ways to earn money when first starting out in affiliate marketing and you don't have to invest any money up front to get the bal rolling.
1) Your first step is to sign up and become approved for Clickbank. You'll want to ensure you already have a quality site ready with plenty of high quality content already in place.
2) Next you will want to research popular Clickbank products to serve up on your site. This might not be so easy if so many others are already offering those same products.
3) After you find the product you want, you can easily create a hoplink on the affiliate resources page or use the premade banners in place by the product owner.
4) Using banners and premade links is not the only way to market Clickbank. You can also create custom reviews of every product.
5) The advantage of using Clickbank is how they will handle the transaction and deliver the product. Your sole job as marketer is to get the customer excited about the possibility of buying that product. All this is best done with high quality content, such as reviews.
If you have other good ways to market with Clickbank, include them here.