My lawnmower stopped working where do I begin to look?

I was mowing the lawn which is about 3 feet high today and the darn thing stopped. I could not restart it and it is full of gas and oil. It tried but doesn't turn over.

Where do I start to look for the cause. I vaguely know it could be the spark plug, carb but little else. I am not a handyman and it takes a while to find someone to help.

If it is a simple fix like spark plug maybe I can do it else I am stuck.

Advice appreciated.

My lawnmower stopped working where do I begin to look?