Browsing Database and Extracting Metadata from Database Tables
As you can see in Externalizing Internal Database Connections and Internalizing External (Shared) Database Connections), in both cases, the context menu contains two interesting items: Browse database and New metadata. These give you an opportunity to browse a database (if your connection is valid) and/or extract metadata from some selected database table. Such metadata will be internal only, but you can later externalize and/or export them.
Remember that you can also create a database table directly from metadata. See Create Database Table from Metadata.