OK, sorry for the "off topic" post...
I took these photos while doing my valve lash adjustment.
This one shows the lever at the back of the valve cover on my Kama. It is operated with a cable that pulls the lever. The lever is attached to a rod with cams on it that when activated, opens up all the exhaust valves on mine.
Below is the knob on the dash which you pull from the driver's seat. Actually, on mine this is the kill knob, but the decompression knob is right next to it on the left. Pretend this is the decompression knob for a visual... I have it pulled back so I can rotate the crankshaft for setting the valve lash.
Now, when the exhaust valves are held open, the engine turns over without any compression. It is easier on the battery and starter motor especially in super cold weather starts. It also allows a squirt of fuel to get into the cylinders, and as the engine is turning over, the oil pump starts pumping to lube the journals, etc. without load on the bearings. Then after a couple revolutions, you let go of the knob and the engine catches.
My Kama starts very easily and really doesn't need that feature. It had no glow plugs and is direct injection. As a matter of fact, it shipped out without the lever connected to the cable. But some other Chinese brands are hard starters and it comes in handy for them.
