"In-house" use of items refers to patrons using items without checking the item out.
Many libraries want to capture this information because it provides a more full-fledged sense of how a library collection is being used.
In FOLIO, an "in-house" use shows in the Check-in app when you see a house icon in the "In-house use" column:
The way this is tracked can be not obvious, since there are not "in-house" use statistics available anywhere in the FOLIO UI yet.
When an item is checked in, FOLIO tracks information about the check-in. This facilitates statistics, displaying item information, and tracking in-transit items. This is also how FOLIO tracks an "In-house item". It assumes that if an item is checked in, and when it's checked in it has a status of "Available", that that is "in-house" use.
You can get that data from your underlying system using an API tool like Postman.
You would send a GET request to the following address (substitute the address of your Okapi instance in):
{{okapiinstance}}/check-in-storage/check-ins?query=(itemStatusPriorToCheckIn=="Available")
If you don't have a reporting tool, you might want to then work on getting that data into a format that can be parsed in Excel. See Use Postman Visualizer to get JSON into a format for Excel for more information on how you could do that.