To join a game, you will need to know the Game ID and password. The game's host will be able to give these to you. Just search for the Game ID on the Join a Game Screen.
To find the Game ID, go tot he game board. At the top right corner of the screen are three dots. Click on this and a menu will appear. Click on Game Information. This will bring you to the Game Info screen. At the top center of the screen is the Game ID. You can hold down on the Game ID an copy it to easily send it to others.
If you choose the wrong square, don't worry. Just hold down ont he square and a pop up message will appear allowing you to delete that square. You can only do this while the board is not 100% filled.
To manually enter a player, go to the game board. At the top right corner of the screen are three dots. Click on that and a menu appears. Click on 'Select a Player'. This will open a window that allows you to type in a name or select another manually entered player. After typing the player's name, select them and hit Close. Now you can choose any squares on the board under that player's name.