One of the most sought after and highly recommended course is this one on Guide to Effective Affiliate Marketing Strategies by Kudus Adu. Not only does he focus on create an affiliate marketing strategy, he focuses on best practices to create money pages, tells you how to build your email marketing list and how to profit from it. He clearly asks people looking for ‘get rich quick strategies’ to stay away from the course. More details here.
Once you sign up to become an affiliate with ClickBank, you will immediately be able to browse the different products available to sell. ClickBank has tens of thousands of products available, so in the beginning it's helpful to search by niche and commission percentage until you locate offers that you want to promote. Make sure you take the time to look at the vendor's sales page before promoting their product. They might be offering a 75% commission rate, but if their website doesn't look trustworthy or put together you aren't going to generate many sales, no matter how much traffic you drive their way.
Two-tier programs exist in the minority of affiliate programs; most are simply one-tier. Referral programs beyond two-tier resemble multi-level marketing (MLM) or network marketing but are different: Multi-level marketing (MLM) or network marketing associations tend to have more complex commission requirements/qualifications than standard affiliate programs.