I realize I'm basically restating what others have said, but.... :blushing:
To me composition is choosing what is going to be in the photo and what is not going to be in the photo, and then arranging those things where you want them. Once you realize that you are doing that each time you put the camera to your eye, you then get better and better at it.
Using the "rule of thirds," leading lines, converging lines, placement of bright areas and dark areas, depth of field, etc. can all be included in composition.
I hope that helps, but I also hope it leads to more questions, because that's how we all learn.
Good luck shooting!