My gas push mower started sputtering and then the smoke stard. I shut it off. Do you know what caused this. Can i fix it?

Broken rings comes to mind, but anything like that is the cause. You have to take it apart to see what the problem is. It's an easy fix. You have to take it apart and hone out the cylinder if the wear is light, but it's best to take it to a machine shop and get them to fit the rings and bearings because they have to hone the crankshaft and cylinder, and may have to machine the head. A valve could have broken and put a hole in piston and so badly scored the walls that you will need a new block. It is sometimes cheaper to find a used motor and replace the rings and bearings after honing out cylinder with a hone you put on a drill.