There are many different ways you can blog. My recommendation would be to buy a domain name, some hosting, and then set up your blog with WordPress.
WordPress is today the most used blog platform in the world, and you can add graphic themes to have a more professional rendering, as well as many plugins which, in a way, will add “functions” to your blog .
Once you have your blog created then it’s time to add content! Your blog posts…
Find one product that you can recommend to people interested in your topic/niche and then start creating content (to use as blog posts for your blog) that directs people to your affiliate link for the product.
You could write a post educating people about the topic of the product and then point them to the product.
You could write a blog post reviewing the product and pointing people to it.
Your options are unlimited when it comes to creating content, but just make sure that the blog post is in some way related to the product and points people to the product through your affiliate link, so that they click and buy it, and you make money.
Your next step will be posting the content to your blog.