Click on the blue Invite Friends button in the FRIENDS window.5.Then, send a message to the friends that you would like to invite to the game and voil!
Call of Duty Warzone is a free to play game. It's not on GamePass and it doesn't need Xbox Live Gold either. MW2 and its multiplayer component is not free. You need to buy it if you want to play the single player game or MW2 multiplayer.