forms – data entry interface?

I'm trying to create a simple web application. In an approach from scratch, I will first create my database schema. From what I understood, the equivalent of db TABLE in Drupal is Content-type.

So I created one, added the fields I needed. It is now time to create a data entry interface. I can see that I can add "data" via Add-Content. But this is heavy and not suitable for the end user.

How to create a form-based interface for an application user to add data (lines).