The Nuxeo Platform framework and its "Layout" module offers many widget types. Some are exposed directly in Studio interface, but some are not. If you want to use one of those existing widgets in Studio when editing a layout, you should drop a generic widget from the "Advanced Widgets" category on the right, as in the screenshot below:
You should then fill the proper type attribute in widget configuration screen (among the existing one or by giving the id of the one you target) and the widget properties in the Custom properties section.
Let's say that the widget needs to be linked to the metadata description from the schema dublincore (prefix dc), you can click on Add next to "Fields" and enter the field but syntax will differ whether you are on a form layout or a table layout.
- Form Layout:
dc:description - Table Layout:
data.dc.description