Why my mower won't start

gas motors require spark, fuel and air to run.

For a lawn mower, that is the order to search for the problem.

You can test the spark by removing the spark plug, connect the lead, and securely connecting the case to the engine metal.

If no spark, disconnect the plug, and test the lead using a long screwdriver with a plastic handle. Better if 2 ppl do this. If you have spark, replace the plug. If you don't, it may be beyond your skill to fix.

If you have spark, then it is likely the carburetor need cleaning or replacement.

That would be evident if there was no fuel smell after a number of pulls.

A blocked air filter may allow it to start momentarily.