After the individual mission folders are unzipped, place all of them into the folder as follows:
Sudden Strike 3 > Media > Missions > Single

Note: very few problems exist with these missions as they have been thoroughly tested as of June 2020, especially on the original disc version of the game and also on Steam. However, they are not tested on modded versions of the game and some are not tested fully to completion as they take so long to complete. Please accept my apologies if scripting mistakes prevent your victory, and consider yourself a winner if you get far enough to encounter one.