As a rule you should start your Motobecane by rolling and pedaling it, but if you find it easier you can start it on the stand.

Make sure that Pulley switch is locked in the M (motor) position.

First turn the petcock on by the fuel tank to allow fuel to fill the carburetor.

Now position yourself on the moped, with your left thumb on the Choke knob on the handle bar, and your right thumb on the Decompression knob bellow the Throttle grip.

Now start pedaling vigorously while pushing the Decompression knob and the Choke knob.

When your hear or feel the engine starting to spin it means the piston is moving up and down in the combustion chamber. You will hear compressed air coming out of the exhaust pipe and from the Decompression valve on top of the engine. 

Now quickly  let go of the Decompression knob and turn the throttle towards you (down) to give it gas, while pedaling still,  when the engine will start running by it self  you can stop pedaling it.

Keep the Choke on until you feel the engine will stay running, it won't take long to warm up.

Not using the decompression knob makes it harder to get the engine to rotate, because the compression has nowhere to go and won't rotate the crank inside the engine.