Basically the engine will turn a variety of different props. Which one to choose depends on the particular application and how you want the plane to fly. Larger diameter props with a low pitch give the plane more pulling power but less top speed, sort of like low gear in a car. Small diameter, higher pitch props give less pulling power but higher top speeds. Those are just general rules of course, you'll always find one that seems like the exception.

Props of different designs and from different manufacturers will perform differently as well even if they are the same diameter and pitch.

The 11x6 that was recommended to you is probably a good all around prop for your engine and general sport flying.

The bottom line though is to collect a few props appropriate for the engine and fly them all then choose the one you like best.<br type="_moz" />