Facebook Places is a way to tag your location on a mobile device. Your friends can also check you in as well, so you may not feel comfortable with everyone checking you in. By default, the settings are that anyone can see where you've checked in. If you want to change that, go back to "Customize settings," go to "Places you check into" and change it. I clicked "Only me" so only I can see where I've checked into. If I don't want my friends to check me into places, I go to "Things others share," "Edit settings" and you'll see it's enabled at the moment - click "Disabled" - there you go. If you would like Facebook to alert you when somebody tags you at a place, you're going to leave this box checked. This is just letting you know that anytime someone comments on one of your check-ins or tags you somewhere, they'll send you an email notification.