What you need to know about copyrights

Some stock images are just for "editorial". There's a little sentence saying that on Shutterstock, for example. If you'll use the image for commercial use it's like taking photos of some random person on the street without their agreement. Editorial use is allowed for newspapers and such.

Read about copyrights.
Check if it's only for personal use, or for commercial use - meaning, to make money out of it. See if the creator asks for a credit or if it's "public domain" so you can do whatever you want.

Read licenses, take time and go over the use that the creator/service allows you.