Drawing terrain
Once you've seen what's already in the level, we're going to start adding some terrain.
Terrain is solid ground, walls, or platforms. It's the stuff that you can walk on and bump into.
To draw terrain, open the Game Objects sidebar, and click on a terrain brush. Now it is ready to paint into your level. Click and drag inside your level to draw terrain.
Think about the way you'd like your world to designed, and draw terrain to match that. Try using different kinds of terrain for different areas.
Note: if you try to place other objects as terrain, you'll need to first select the tile map (see step 7).