You find the checkouts either on the dashboard (recent and overdue checkouts) or at the checkouts page by selecting Checkouts from the main menu, then List Checkouts.
You can also go directly to an item that has been checked out, select the Activity tab, then Checkouts.
Find the checkout you want to check in, and click either the icon to display checkout details and select Check in from there, or click the icon to check in directly.
All items in the checkout is selected by default. If the checkout contains more than one item, and you only want to check in some of them, you can un-check those you want to leave out to check in later (partial checkin).
You can also add remarks to the checkin.
Click Check in to check in the selected items.
The status of a partial checkin will remain as checked out until all items are checked out. Repeat the prosedure until all items are checked in, to change the status to the checkout to checked in.