Extract the archive's contents directly into the folder the game is
installed in (usually C:\Program Files (x86)\Steam\steamapps\common\Sonic Adventure 2). Place your mods in the mods
folder, then run SA2ModManager.exe. Check any mods and codes you want
enabled, and edit the settings as desired, click the "Install Loader"
button, then click the "Save & Play" button to start the game.