When I try to run my lawn mower, I pull the "string" but it dosen't make any noise, I have repeatedly tried, but it dosen't work. Would I need to buy a new lawn mower or is there a way to get it to start working.

Unless you have tools, and know how to use them... might be beyond your abilities. You need fuel, ignition and compression. Lack of any of those three will give you what you see. You have to figure out what is missing and correct it. Unless you have a REALLY nice mower, it will cost you nearly as much to fix as a new cheap one will cost if you have to take it to a shop.

Compression you can feel pulling the recoil starter....the other two you can figure out removing the spark plug after trying to start it.

Is plug wet? If so getting fuel. Does it have spark?

Sheared woodruf key on flywheel from hitting something is common...but it usually still tries to fire even if it won't run so I think that is unlikely.

Pull it over a few times..pull spark plug, see if its wet, and holding it against the engine pull it a few times and tell us if you see a weak yellow spark or a blue one...or nothing at all?