Opening an affiliate account is simple. First, go to the website of an affiliate program like Amazon Associates, ClickBank, or ShareASale. Next, fill in the sign-up form with your details, telling them how you will drive traffic to the product and get approved. Once approved, you'll be allocated a trackable link. You put it in your content and start earning commissions from sales. A very small number of programs can approve you right away while others will need to thoroughly review it.
My first affiliate account was with Amazon Associates. The registration was uncomplicated and they accepted me within a short time. It was no big deal to add affiliate links to my blog and social media. The trick here is to be explicit about how you will promote products when filling the form.
I had few sales with Clickbank and I'm so happy about it. I think I was able to achieve that because they offer more specialized digital products, which are highly commissioned than the physical products.