A check-in is a recorded activity on an item. Check-ins happen at locations.
Every time you check in an item at a location, you add another piece of history to the item. This includes the Item ID, the location, time, and the user.
There's a bunch of check-in types - Create (from Scratch or from Item), Receive, Move, Combine, Send, and Destroy - that let you build a detailed history of your items.
Select the location where you are checking in the item of an Item Type that has been added. The Location tab is located in the menu on the left side of the screen. You will need to have a Location that has been added with the types of check-ins you want to be able to do there.
Check in something!
From within the Location, click the Check-in button and then select from the tabs which type of check-on you will do. You can move, combine, send, or destroy only items that have been earlier created or received.
Other great tips about check-ins: