How do I make (or input) categories on the left sidebard?
To create a sidebar with categories on the left you will need to get the direct affiliate links to the categories from your Amazon affiliate account and add them to your sidebar.
See the video below to help you to create a sidebar on the left.
Here’s a video to help you with this:
Also, here is a link with many resources to help you with creating a WordPress menu with custom links: https://www.google.com/search?q=how+to+create+wp+menu+links&oq=how+to+create+wp+menu+links&aqs=chrome..69i57.6210j0j7&sourceid=chrome&es_sm=93&ie=UTF-8#q=how+to+create+wp+menu+custom+links