A 'level' in Planar is just a separated part of the runtime, in that everything gets cleared when you load a new 'level' - other than that there is just to tell you that Level files are just load files, but that there are lots of nice functions to make creting them easier
Planar supports have a single specific background image during gameplay (which the user can manually disable if gameplay is slow or they don't like) which is literally just an object with the name 'background'. There are a few load functiosns built around it:
The text file data/loads/normal.txt is loaded by every main level. It sets up the player for you, with this typical red suit and black hat, approprite size, animations, mass, stength and (in the future) sound effects. The only thing you need do with the player is set his starting location. The 'player' is just a body called 'player'