It took me a little bit to figure it out too. I found out about it through Etsy. Like sgtiger, I use it a lot to bookmark interesting items or ideas.

You can also follow other peoples pins. One woman that I follow pins photos of woman's clothing from the 1800s that are lovely. Another pins old photos - anything & everything, from street scenes to family portraits to circus freaks to silent movie stars - that are just so interesting.

You do have to be careful tho! because it can be a time sucker.