Clock starts on the ready or the snap?

[mikesears]

For NF: I was under the impression that, after a penalty, the clock starts as a result of what happened during that down. If the kick went out of bounds, then the clock wouldn't start until the snap. Am I thinking of the wrong down? What would happen if on third down, the clock was stopped and this situation happened on 4th down?

I am confused about when the clock stops and starts following a penalty. Any help on understanding this would be GREATLY appreciated!