Find affiliate codes and paste them into your site. Once your site is well-established and respected for its content, you can begin to link out to affiliate programs. Search the various affiliate networks and look for products that relate to the theme of your website. Grab the affiliate code from your account and paste it into your site. As people visit your site and click these links, you can begin earning money from the referrals in your articles.
Theme – you don’t need a special theme for affiliate marketing, you probably just need a blog. I recommend StudioPress themes since that’s what Yoast, Matt Cutts (from Google), and I use. Matt Mullenweg, founder of WordPress also recommends them. One of the biggest mistakes I made was using a theme from Themeforest… since they’re built by independent developers who may stop making updates to their theme. This happened to me and I hear horror stories all the time about people having to switch themes and redesign their entire site. I’ve been using the same StudioPress theme (Outreach Pro) for 3 years. Their themes are lightweight (load fast), SEO-friendly via optimized code, secure, and they have a huge selection of plugins for the Genesis Framework and an awesome community in the Genesis WordPress Facebook Group. They include documentation for setting it up and will serve you for many, many years.