Here is the simplest step-by-step instructions I can give you.
1.This is what the zip file looks like. I don't use WinZip, or WinRar, just the Windows default compression thing.
2. Extract the zip file to your steam\steamapps\your e-mail\Half-Life directory, and all the files will automatically go into the right directories. I believe the model replaces Vegeta, so in order to play as Brolli, select Vegeta from the character menu. He will still have all vegeta's attacks, it will just be Brolli's character,
*note* This is just a model, not an entire character replacement.