Fortunately there are tons of free blogging platforms out there. You can check out a comparison of them here, including WordPress, Tumblr, Medium, LinkedIn and Weelby.
For an affiliate website, I recommend using WordPress. This will look the most professional, and give you the most control over your articles/how everything is set up.
Medium, Tumblr and LinkedIn, on the other hand, are great for their built-in social network. It’s much easier to get followers on those platforms more quickly than via WordPress.