This is a diagram of what's known as N-Tier Archicture.
It's premise is that you can attach N number of applications all calling the same codebase and database.
You can see the database on the top-right, connects to the API, and then we have web applications, tablets and phone apps all
calling this same API and database.
Most "full-stack developers" start with the application and use lazy ORMS to build the architecure (eg entity framework).
We begin in the top-right ... with the database.
By doing this bit right, everything flows through better and is less expensive in the long-term.
Doing it the other way will probably be quicker in the short-term, but you'll be calling us once your business grows
to scale and fix your database, which will often be far more expensive.