Version v0.40 of Metabase is no longer supported. Check out the docs for the current stable version, Metabase v0.63.
How do I answer questions where I need to join tables together?
If you’re using Metabase version 0.32 or earlier, you’ll need to either write a SQL query that contains joins, or have your Metabase administrator set up foreign keys (they can read more about that here).
If you are using Metabase 0.33 or above, you can perform joins using the Notebook editor, but you should probably upgrade anyway.
Read docs for other versions of Metabase.