Earlier today Facebook finally announced the official launch of Facebook places. Mashable , ReadWriteWeb , and others covered it live, but if you missed the announcement, here’s what you have to know.

BTW, one thing no one is talking about yet is Places within the Graph API . You can query recent checkins by users, pages, places: GET https://graph.facebook.com/[place/Page/user_id]/checkins

That alone is SO powerful!

Anyways, starting today, you can immediately tell people about that favorite spot with Facebook Places. You can share where you are and the friends you’re with in real time from your mobile device.

Checking In with Friends

Ever gone to a show, only to find out afterward that your friends were there too? With Places, you can discover moments when you and your friends are at the same place at the same time.

You have the option to share your location by “checking in” to that place and letting friends know where you are. You can easily see if any of your friends have also chosen to check in nearby.

To get started, you’ll need the most recent version of the Facebook application for iPhone. You also can access Places from touch.facebook.com if your mobile browser supports HTML 5 and geolocation.

Go to Places on the iPhone application or touch.facebook.com site and then tap the “Check In” button. You’ll see a list of places near you. Choose the place that matches where you are. If it’s not on the list, search for it or add it. After checking in, your check-in will create a story in your friends’ News Feeds and show up in the Recent Activity section on the page for that place.

Places is only available in the United States right now. But we expect to make it available to more countries and on additional mobile platforms soon.

Checkin Friends

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. You can post an update along with your check-in to tell people more about what you are doing.

In the “People Here Now” section, you can see others who are checked in with you at that place. This section is visible for a limited amount of time and only to people who are checked in there. That way you can meet other people who might share your interests. 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.

The next time you head off on vacation or go to a show, check in with Places to find out which friends are there. See who is close by and read the comments from other friends who’ve been there before.

Tagging and Control

With Places, you are in control of what you share and the people you share with. You choose whether or not to share your location when you check in at a place. When you check in, you can tag friends who are with you but only if their settings allow it. When you are tagged, you are always notified.

Only your friends can see when you visit or are tagged at a place, unless you have specifically set your master privacy control to “Everyone.” You also have the choice to set more restrictive customized settings.

When a friend tags you through Places, you will receive a notification on Facebook and on your mobile device. The first time this happens, you’ll be given the choice to allow your friends to check you in to places.

When your friends check you in, it is as if you have checked in at that place yourself. You also will appear checked-in to your friends. If you do not allow friends to check you in, then when they tag you at a place, your name will appear in the same way it appears in a tagged status update. You will not appear checked-in at that place.

You can always remove any Places check-in or tag using your mobile device or on the web. It’s like removing yourself from a photo tag. You also have the choice to turn off the ability for friends to check you in at Places. Go to your Privacy Settings and turn off the setting to “Let Friends Check Me In.”

You may want to share your check-in information with third-party applications that build interesting experiences around location, such as travel planning. Applications you use must receive your permission before getting this information. Your friends will be able to share your check-ins with the applications they use to help create new social experiences with location. If you don’t want to share your check-ins with your friends’ applications, just uncheck the new box in your Privacy Settings under “Applications and Websites.”

Everything happens somewhere. Start exploring your world with your friends by sharing your experiences at the places where you go. Take a tour of Places to learn more.