Importing data into an existing application

I want to create an application with multiple linked tables (forms, right?) and I have the data all set up in Excel spreadsheets. I imported the first table (form) easily enough when I created the application. Now I want to create additional forms, yes? And import the other spreadsheets into the new forms -- but I can't figure out how to do it.

Am I missing something, or is this not supported yet?