Engine won't start oil level is good has fuel
Remove the spark plug and attach the plug wire to the top of the plug. Place the base of the spark plug against a metal part of the engine and pull the starter cord. You should see sparking between the plug electrodes. It helps to do it in a dark area, not out in the sun.
If there is no spark, something may be shorted out, a wire broken, or the magneto has come apart, etc.
If there is spark, then the problem is fuel related. The gas may not be getting to the carburetor, or the air / fuel ratio is wrong, not allowing combustion.
You have to eliminate each of the possibilities one by one. I would recommend buying a can of starting fluid, which you can get at parts stores, Walmart, Target, Shopko, etc. Spray a little in the carburetor or directly into the spark plug hole. Replace the plug and if it acts like it is starting, then dies, you know you have good spark and the problem is with the fuel or carburation. If the machine has sat for a long time with stale gas in the carburetor, it gets gummed up and will not start. The carburetor will have to be removed and cleaned.
Good luck!