You can invite friends to join your Group when you play online. When you are online, create a Group by pressing on the social menu below the currencies on the top right, and then click the "Create" button. You can then share your Group Code, select your friends from your Game Center friends list, or select players on the same Island as you under the Recent Players tab. If your friend has shared a code with you, press on the social menu and click "Join" to enter their Group Code. You can only invite a maximum of 3 friends. You can also add friends to your Group from the HoloSim Lobby and pressing "+" button.