How do I add friends in Mario Kart Tour?

To add friends in Mario Kart Tour, one must first complete the initial tutorial to unlock the Friends feature. Once that's accomplished, access the main menu by tapping the menu button at the bottom of the game screen. Navigate to the "Friends" icon which will lead to the friends list. Here, one can send friend requests using the "Add Friend" option by entering another player's Nintendo Account ID, a 12-digit code unique to each player. If someone else sends you a request, it appears in this same area under 'Pending Requests', where one can accept it. It's an easy and straightforward process to connect with others and enjoy competitive races together.