There are 2 ways to check in an item when it is returned:
1) Place you cursor in the "Check-in Date" field. If you double-click it will enter today's date. If you want a different date you can select one off the calendar (which will appear on the right of the field) or just type in the date.
2) Use the Quick Check-in menu. (see Quick Check-in here).
Once the Check-in date is filled the "Current Location" of the item will change to "Checked In" from "Checked Out".
