These rewards usually come by way of referral incentives, such as product or service discounts or free access to an app or program that would otherwise cost money. While there are upfront costs to companies initiating a referral program in order to cover the cost of the reward, it can greatly increase long-term revenue by making loyal customers from an existing customer base and by bringing in new customers (who, in turn, may refer friends as well).
The very first step to getting started with affiliate marketing is to choose a niche (or "vertical" if you want to sound super knowledgeable). This niche is what you're going to "stock your store" with. And we're not going for a general store vibe here. As an affiliate marketer, you want to be known for something.

There are more players than several years ago, and now there are many tools that can quickly uncover the traffic sources and keywords of a publisher. With a tool like Semrush, you can quickly review all of these, plus many more.
I know you will want to put your affiliate links everywhere and hope that someone would buy from you but this is not the right way.