Hi there, Stephanie - welcome! To relieve you of any skepticism: this is a legitimate way to complete tasks and earn money on the side, yes. Much like anything else, you've to invest your time and energy, but it's ultimately worthwhile.
One way of getting more bang for your buck is to plan a route. Then try to do as many shops along that route as possible. I throw everything into my GPS (or you can print from online maps) and then just drive from one shop to the next.