From USAJOBS Help
Agency Search
Select an agency by clicking inside the “Choose Agency” box, scrolling through the selections, and clicking on your choice.
Once you select your desired agency, go to the “Then sub agency” box to select the desired sub agency. You can also select to view all jobs from the main agency and then click the “Add>>” button to add them to your search. Please add no more than 10 search criteria for Agencies.