Download .net from https://dotnet.microsoft.com/download/dotnet-core/current/runtime and restart computer.
Download Depot Downloader from the files above and extract to any folder.
Put downloadbeatsaber.bat into the extracted depot downloader folder and run it.
Input a manifest id from here and input your Steam login name and Password with Beat Saber Purchased.
If youre using older version then download simple-converter from the files and drag song folders over the exe to convert to the old song format.
Youre on your own on finding songloaders but I just look up "Beat Saber Mod Installer" and use the links from Umby's github such as SongLoader and using Mod Assistant for the versions past 0.13.2