Hello, is there a guide that shows all the art/tools available in the game? I have played most of the campaign I think and still don't have a thin straight line or many other things I see other people using to design in community levels.
There's a HELP menu in the editor that shows the more advanced controls. Most of what you're seeing with things like straight lines are done with the corner select tool, allowing you to stretch/manipulate basic objects like boxes and turn them into thin lines.
Snap to grid ON also helps.
Additionally, Daftbomb created a level tutorial that shows some of the advanced techniques.
You can search for it in game or here with a web link. If you sign in with your PSN ID, you can queue it and it will appear in your "Favorites" in your community profile in the game.
Of course feel free to post questions here. Lots of good creators read the forum.