The most important thing a newcomer to affiliate marketing needs to focus on and learn is *how to generate a large and engaged audience*. Without a large and engaged audience, or the skills to grow that, then affiliate marketing will be completely ineffective. Learn one top-level acquisition channel (partnerships, SEO, whatever) and then learn the middle of the funnel with marketing automation/email marketing to further convert people time and time again to different offers once they are within your network.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.