Open windows search Bar, or press Windows Key + R to open the Run Box, Type %appdata% Enter, you will able to see Red Alert 3 inside, click in, there was Maps Folder inside. If the Map name is ABC, then create ABC folder inside the Maps folder. Unzip the file you download into it. E.g. Maps > ABC > Inside ABC folder should be all the files, e.g. ABC.ini, ABC.tga