Cropping v resizing?

Think of a single magazine page as your whole image.

Cropping is like taking scissors and cutting out that one coupon in the bottom-left corner you'd like to use, throwing away (or just leaving behind) the rest of the page. The size of the coupon has not changed - you just have less of the page than you did before.

Enlarging is when you take that magazine to be photocopied, and you tell the photocopier to make you a copy of that magazine page and blow it up to the size of, say, a poster or two-page spread.