Pinterest is like a huge global bulletin board where you can pin images already on there, images approved for pinning (some sites suggest you pin things) or your own images. You can't just take people's images though because that would be a breach of many rules so if you're in doubt leave it out!
(You have to be invited to join pinterest so if you're not on there and you'e curious...e-mail me via the contact form on this site and I'll invite you.)
Here are my boards....
As you can see I have them for a variety of topics - American readers did you know we don't have crescent roll dough in Australia? Shocking I know, but if we ever do I have a whole board of recipes ready to go.
As a writer people have often cut magazine images of pictures that remind them of characters or sttings or to inspire them. Now you can do that on Pinterest. I have a board for Hearts Afire as you can see and for another of my novels called A Fair Exchange
In Hearts Afire the main character Cassie is a caterer and a bride so I have collected images that speak to that. Jack is a fireman so more pictures along those lines. And there is a tropical island as well. I think you get the idea.
in the same way writers use music to inspire them images can really help. If you're sitting in winter in Sydney sometimes you need a nice sandy beach to look at to get you in the mood to write about one.
Like anything you can use these things to help you, or they can be another massive tool for procrastination...hopefully I'm using Pinterest for the former.