Your server is the back-end. Your app is the front-end.
Your app contacts your server by making API requests.
Entering data app:
In this app make the interface for entering the data, and submitting the data to the server by a POST API request. In the server take the data and save it to the database
Performing Operation App:
In this make the interface for other CRUD operation and let them talk to the same server using other API routes for requests. In the server corresponding to each route perform the operations