Composition is the positioning of the elements of the photo. Basically, look for a way to make the photo interesting and lead the viewers eyes to where you want them.
Here are a couple of articles that you might want to look at:
Digital Photography Composition Tips - Digital Photography School
5 Elements of Composition in Photography - Digital Photography School
5 More Elements of Composition in Photography - Digital Photography School
Framing Your Shots - Photography Composition Technique - Digital Photography School
As for the settings - aperture, ISO, and shutter speed - these are used to control the exposure.
Start with this info on exposure:
Learning about Exposure - The Exposure Triangle - Digital Photography School
https://vimeo.com/48016137
I suggest that you spend a little time on Adorama's Learning Center site (free info) - a quick way to learn a lot : Expert photography blogs, tips, techniques, camera reviews - Adorama Learning Center