To play Brutal Doom, first you'll need a sourceport: in this case, either GZDoom (https://zdoom.org/downloads) or Zandronum (https://zandronum.com/). GZDoom is probably the better choice though.

Second you'll need the IWADs (basically the mapsets, textures... of the game) to play/speedrun which mean buying Ultimate Doom or Doom 2 or Final Doom on your favorite gaming platform.

Finally you'll need Brutal Doom: there is a lot of versions basically everywhere on the internet. The latest version is V21 (https://www.moddb.com/mods/brutal-doom/downloads/brutal-doom-v21-beta). The most runned version is V19 (http://www.mediafire.com/file/cpu3x42q58va416/brutal19.pk3). You can play any version really but I'll personally stick to those two only.

Drop the .wad and the BD.pk3 files into your sourceport folder and you should be set. :)