The game is the most fun making you own levels! Try the default one (though very broken) for a little bit, and then try making your own.
The game will always load assets/level.json, to create your own level replace it's contents with { "blocks": [] } and open the debugger. If you want to have multiple levels, you can have multiple files and chose one by renaming it level.json.
W/A/S/D: MoveSpace: JumpEsc+Esc: Open debuggerRight click: Place/edit blockLeft click: Delete blockTab: Toggle fly1/2/3: Rotate plane 90dCtrl+S: Save levelArrow up/Arrow down: Move cross axis