Post Filtering by GET URL parameters

I am trying to add a simple filter for posts in my wordpress site by setting parameters in the URL, however it is simply not filtering the posts which is driving me crazy. All the tutorials or forums dont show what happens if the URL isnt filtering your posts.

My posts have categories (Test, windows and WordPress) that I would like to learn to filter, e.g. it would have checkboxes for each category type. However, when the URL is set as /sites/?orderby=date&order=DESC&category%5B%5D=windows it isnt changing anything that is displayed?

If someone could help me out to understand why its not filtering the posts that would be appreciated.

My code: