How to search by metadata

How do I search documents by metadata, so that I can look at, for example, only documents that contain a certain character or location?

In the project search box (the search field at the top right of the screen), click on the magnifying glass and you’ll get a drop down list with several options, including the ability to limit your search to say ‘keywords’, ‘status’, ‘label’, ‘synopsis’, and even (I think) ‘custom metadata’.