I don't know that engine specifically, but engines need fuel, air, and spark to run.
A 50cc motor is likely a two stroke. Two stroke motors literally burn oil to lubricate the cylinder. That bike either has a gas tank, and a separate two-stroke oil tank, or you have to premix the two-stroke oil into the gas. Make sure you've got fuel in the tank, and the petcock, if it has one, is turned to ON.
Unscrew the spark plug and connect it back to the plug cap. Insert the spark plug between two cylinder head cooling ribs so that the outer ring touches the ribs. Now kick the starter a couple of times and observe the spark. It should be blue and strong.
If you don't get a spark, check all wires for damage, and make sure all connections are solid.
Visually inspect the airbox and air filter. The air filter should be reasonably clean.
Start there, and post your results.
2004 BMW R1100s
(previous rides: 2008 R1100R, 2000 Hayabusa, '83 V45 Sabre, '98 Buell S3T, '95 CBR600F3, '83 KTM250)