I have sublime text 3, but after I installed sublimelinter-html-tidy through the 'Package Control: Install Package', nothing changed. I also have Emmit, Bracket Highlighter, Side Bar, and a few others installed on my Sublime 3, and they all do what they are meant to do. They work. Only sublimelinter-html-tidy doesn't do anything, even though it is in my instaled packages.
Any help, or if someone could point me in the right direction, would be great.
When installing new packages, I strongly suggest reading the documentation on packagecontrol.io. In the case of SublimeLinter-html-tidy, you will notice that there are two prerequisites: SublimeLinter3 and tidy. First, though, please read through the SublimeLinter docs to get an idea of what the plugin is, how it works, and how to set up specific linters. Make sure you read the installation instructions. Next, install and set up SublimeLinter via Package Control.
In order for SublimeLinter-html-tidy to work, you need to have tidy installed on your system. The instructions are in the docs I linked above. Once it is installed and you have verified your PATH as described in the SublimeLinter docs, you'll need to configure tidy. Documentation is here.