Over the summer, Instagram took a page from Snapchat's playbook when it launched Instagram Stories. Now, Instagram's parent company, Facebook, is taking a cue from another powerhouse: Craigslist. Today, Facebook is launching Marketplace, a new vertical on the app where you can buy from and sell to people in your specified area.If this sounds familiar, that's because Facebook has played with the concept before. In 2007, the desktop version of the social network introduced a classifieds marketplace where you could list items. But this is the first time that something like it will be available on the app.In a blog post about the new feature, Facebook explains that Marketplace is a natural step, given that people are already using the app for similar purposes. Over 450 million people are buying and selling products within Facebook Groups, so it makes sense for all of those activities to be consolidated into one area.Marketplace will start rolling out today to people in the U.S., U.K., Australia, and New Zealand. The one somewhat odd caveat is that it's only available to people over 18 years old. What about high schoolers who want to buy used textbooks for college? (At least they can still go to Craigslist.)Click through to see what Marketplace looks like and how to use it.