URL or link shortening is used predominantly on social media to enable long urls to fit within character restrictions (and to make links look nicer too). You should use shortened links in your social channel bios also. These are the main benefits of using link shortening. However tracking of clicks via that short link may also be beneficial to you
There are many URL shortening service such as Bit.ly, Google URL Shortener, TinyUrl, Snip.ly, Rebrandly and others. For the most part all you need to do is paste your affiliate link into the specified area. The provider will then create a shortened link for you to use. When clicked, this link will redirect through your affiliate link and onto the merchant site.