1. after downloading blender, click the 'download' button at the top of the page.
2. open file explorer, open 'downloads' to see the .py file you downloaded from here.
3. create a new and empty folder. drag the .py file into that folder
4. open blender, click on 'edit' then 'preferences..'
5. click on 'add-ons', the arrow at the top-right, then 'install from disk'
6. your files should pop up, click on 'downloads' (or whatever section you moved the .py folder to), then double click on the folder that contains the .py file. click on the .py file itself then "install from disk"
7. you can exit preferences and if you open it again "Roblox Animations Importer/Exporter" should be there