Step - 1
Understanding what you want to do, and what you have is essential before you can dive into designing a database.
Step - 2
We specify the entities, columns, and their relationship. We may use an entity relationship (ER) diagram to visualize the database.
The output is: A conceptual schema (described using a conceptual data model like ER model).
Step - 3
It’s concerned about data model mapping; mapping a conceptual schema (like ER model) into logical schema to provide a much detail description.
The output is: A logical schema (described using a logical data model specific to the DBMS like relational model).
Step - 4
It describes the details of how data is stored. You start by defining (already modeled) tables, how the data is stored, define relationships, … in DBMS.
This requires dealing with the DBMS, and could involve SQL.
The output is: An internal (physical) schema (described using a physical data model).