All grants are loaded into the game additively (so none will be overwritten), but only the first instance of any grant will be loaded if there's more than one with the same name. It's worth noting that as of Alpha 24, any new Grants will be loaded in the order of installed mods. Updates for the mods will be downloaded automatically.
Then, when you go into the game, you will need to activate it through the mods tab in the main menu. If the mod is part of the Steam Workshop, you need to go to the workshop page of the mod and subscribe.
