To import files from your local storage:
Click + ADD BASE at the top of the Bases page, where all the bases in your workspace appear.
Choose Import from the dropdown menu.
From the pop-up menu that appears, choose Local storage.
From this pop-up, you can browse through your local storage, with compatible files highlighted for you. Click Open.
All the tables and fields from your files will then be listed in the pop-up window. Just customize your data, click IMPORT in the top-right corner of the pop-up window, and you're all set!