Composition is how the Elements of Art and Design - line, shape, color, value, texture, form, andspace - are organized or composed according to the Principles of Art and Design -balance, contrast, emphasis, movement, pattern, rhythm, unity/variety
Your first roll of film was assigned to use Line, shape and texture as your main theme for photos. Your second roll of film was to use the Rule of Threes or Odd numbers:
There are many Rules of good composition, the "Rule of Odds" (also there is one called "the Rule of Threes" which is the same thing...) suggests that an odd number of subjects in an image is more interesting than an even number. Thus if you have more than one subject in your picture, the suggestion is to choose an arrangement with at least three subjects.
Examples of good composition using 3 objects or subjects: