If you start building your obby above the grey baseplate, your player will just fall harmlessly onto the baseplate rather than dying when they miss their jump. That doesn’t exactly give your player the challenge you want them to have. To remove the baseplate, you’ll need to use the Explorer window.
The Explorer window is typically to the right of your workspace and lists all the objects within your game. You can use the Explorer to select and work with parts in your game, even if you can’t find them in the 3D view.
Click on the Baseplate and delete. On a PC, you can also right click or on a Mac, you can two finger tap.
The first thing to do when creating a game is determine where players start. The SpawnLocation is where a player appears in the world at the start of the game or after falling off a platform. Without a SpawnLocation, the player might appear somewhere randomly and fall to their doom.