In the above diagram, we have taken an application, which uses a form to take user information. The information can be "name", "date of birth", "username", "password taken by user" and so on. We have created a button called "Register". When this button is clicked, all the checks are done. What I meant by that is, all the input fields are made sure they are not empty or there are not whitespaces in the password field and so on.

Once everything goes as per the flow (if everything is confirmed and done), event is triggered which runs "function associated with Register button eg: registerUser function". This function helps to send "username" and "password" to API (Application Programming Interface).

But how does front end application knows where "API" is ? Simple answer to that is, the application uses "baseURL" which has domain address off the API. Now, the API also checks or validates "username" and "password". It makes sure that none has taken that "username" before.

If the validation in the API (web service) is done, now it is the time for "Stored Procedure". It means: we are storing that information in API to "Database". The connection with database is done through "connection string" in API. This is the long string which identifies the address of the database.

This is the simple explanation of how data flows from frontend to backend with form registration example.