Say the daughter of your favorite musician just enrolled at your school. If you just use her to get to meet her rock star dad, that's pretty unkind.
Use is an old word with a lot of, well, uses. You can use a bike to get to school, or use up an entire tube of toothpaste in one vigorous brushing session. You might have to show Grandma how to use the 3-in-1 remote control. As a noun use means "purpose." As a verb, use means either "put to work," or "work something until there isn't anything left," unless you use your friend, meaning you exploit her.