Facebook launched their location-based check-in service dubbed "Facebook Places" using Bing Maps to pinpoint everyone's location-based experiences on Facebook.com. When using Facebook Places from mobile device, users will have opportunity to check-in to a specific place of interest. This basically is a location update you provide your friends where you're.
So, fire up Facebook iPhone app or go to touch.facebook.com on your moblie device. Select "Places" button, find location where you're and check-in, which'll flow to your Facebook profile complete with a Bing Map, pin of your location and any commentary you've added to your check-in. Places also includes ability to see where your friends have checked in, a link to get directions to a place (via Bing Maps) and Like button for respective place page. The place information bubbles up to actual Places page which has a larger map experience, plus an update for you to see all of your friends who've visited that location. This means you can see where your friends are checking and discover new places.
When you check in, you can also tag friends who are with you, just as you can tag a friend in a status update or photo. In the "People Here Now" section, you can see others who are checked in with you at that place. If you prefer not to appear in this section, you can control whether you show up by unchecking the "Include me in 'People Here Now' after I check in" privacy control.