Cloning can copy one part of the picture onto another part of the picture. I think you hit ctrl and click the area you want to copy, then click around the area you want to copy it too. It is helpful if you want to remove some small piece of garbage from a scene for example. It is much more time consuming if there is a large object. You clone something that you think looks like what is behind the thing you want to take out.
Also, if you want to try selecting things and changing them in the future, after you select it, try feathering the selection. You can play around with what settings to use on the feathering, but that should help take out the hard white line.
I agree that the original has a nice enough color, you'd rather the attention be drawn to the people rather than the sky. On that note, I think a profile crop that took out the pole would be a good idea too.
It is a very nice and natural pose! I like the way they're obviously posing for the photo, but are not doing the standard toothpaste smile, it is more relaxed and comfortable.