Use the arrow keys to move. Click "Editor" to go to the editor. In the level editor, click empty spaces to add a block. Click any block to delete it. Do not delete the border, though, or else...
Just a test to see if I can make a level editor. This is also my first project that randomly generates textures for a raycaster. If you'd like, you can look at the "Regenerate Textures" custom block to see how I made the random textures, so that you will no longer have to spend a while trying to make good textures for your raycasters.