To add to what mlinder has already said, you also need compression. The air and fuel need to mix together in the right ratio and the spark needs to be delivered at the right time.
Spark:
You need
- battery
- correctly wired & functioning electrics
- spark plug
Read you manual on how to set the timing. Basically, you need your points to open or electronic ignition to trigger when your pistons are a few degrees shy of TDC. What type of ignition do you have, points or electronic?
Compression:
You need a tester for this. If you have one GREAT, otherwise let's skip this discussion for now.
air/fuel:
You need properly adjusted carbs, but I'm sure you knew that. Adjusting carbs takes talent, skill, experience and a little black magic. If you are like me and lack all that and are also short on luck, then meticulous adherence to the instructions in the manual will have to do. If your goal is to just hear a your engine kick over for a half dozen cycles or so, then you can fake a decent air/fuel mixture with carb cleaner or starting fluid. Don't get carried away as this stuff isn't real friendly to your engine, which is designed to run on petrol, not ether.