This is a pretty simple manual-leveling gcode for the Ender 3. The gcode is designed to avoid crashing into the bed clamps (regardless of clamp position), therefore it moves up before initial homing and the leveling points aren´t as close to the corner as other leveling procedures.
There are 5 homing points: One near each corner and one at the center. When the first point is leveled press the wheel under the display to move to the next point.
The "Empty.stl" file is not suppost to be downloaded, it is only there because a thing needs at least 1 3d model before it can be uploaded.
To avoid mechanical damage and inaccurate homing make sure that when the nozzle is at Z0 the bed doesn´t touch it (I recommend lowering the bed quite a bit before leveling) and that nothing is in the way of the print head before starting the gcode.
Scematic of the procedure