How to check people in:
With Facebook Places, users will be able to check in to a location (i.e. a park, bar, store, or restaurant). That check-in will then appear in your friends' news feeds, as well as under the "Recent Activity" section on the Facebook page for that place. You can tag friends in your check-ins using the @ symbol, as is currently possible with photos or status updates (you friends then have the option of accepting or rejecting your tag). With Places' "People Here Now" feature, you will be able to see other people, including users who are not your Facebook friends, who have also recently checked in to your location (although this can be disabled) Facebook explains, "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." Minors will only see their friends.
Having struggled with privacy issues in the past, Facebook is trying to strike the right balance with "Places." Under the default settings, your check-ins will appear in your profile, in your Facebook friends' news feed, and in the "Recent Activity" section on that place's Facebook page. Friends can check you in to places by tagging you in their check-ins, but you have the option of disabling this--As Facebook explains, "The first time this happens, you'll be given the choice to allow your friends to check you in to places. [...] 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."
Mashable highlights how to change your privacy settings: If you want to change whether or not others can check you in without your knowledge or permission, you’ll have to click “Customize settings” on your privacy page, then scroll down to the “Things others share” section. You will note that by default, you enable others to check you in. You can disable this setting; there’s no option to allow checkins-by-proxy on individual approval.
