when I try to run quake I get the error "W_LoadWadFile: couldn't load gfx.wad" how can I solve this problem

I can't remember exactly. I think it's cause you don't have the right .PAKs in the right folders. Make sure you have PAK0, PAK1, PAK2 in the id1 folder. One of the PAKs you will need to copy from your steam/GOG version of the game.