When starting a new game in Sandbox mode, which is what this article is assuming, the save game name does not have to remain 'default'. Click the 'Start New' button to start a new game.

If it DOES have a GameData folder, they intend for you to copy it to your main KSP install folder, and your computer should tell you that the folders have the same name and ask if you want to merge them, you DO what to do this. By selecting the Start Game menu item, the Start and Load Game menu will appear. If it DOES NOT have a GameData folder anywhere in the file you download, you want to put the whole thing inside your existing gamedata folder, rar file but this might be a different file extension or something, but the basics remain, this file you download should have a folder in it marked with the name of the mod, or it might say just GameData, if it says the mod name, go inside it to make sure it doesnt have a Gamedata folder inside of it. When you download mods they usually come zipped in a. Wherever you have KSP installed, inside the main folder you should see one marked 'GameData' inside of which should be a folder marked Squad. I dont have a mac nor have i ever used one so i dunno what the file explorer looks like or anything, but i happen to know that the game isnt built vastly differently on mac vs PC. Literally the exact same place as every other version.

Mod button ksp mac