Client/Server App and DB server development

I have Android App and an Internet server. The source code of the App is ready. However, I am looking for someone to modify it to be an ordinary client/server application for the goals explained in down paragraphs.

The source code of the App has two windows. First window is a login which is supposed to communicate with an Internet server for user registration. Second window communicate with an Internet server to fetch some data. The App sends a particular request and the server responds. We need to activate the first window (registration) and we need to do some changes on the second window. It is currently sends the request through encoding it into the URL. We need to change it and make it like a traditional client/server query response theme.
The first window I need it to handle the user registration process, where the user enters his ID (something like employee ID) and his going to receive a pass code into his email. Then, to complete the registration he needs to enter the correct pass code. Thereafter, the registration window is no longer appear. The second window, should has a circled 3D button and a space to enter 10 digits. This window sends a request to the server the server responds however, the server response message needs to be hidden, just the button changes its color from red to green which means he gots a response from the server. Another small button for other purpose.

Also, I need to program/build the server side. The server is a ordinary server which has a database to enter the employees information with some ordinary columns like employee info, task ID, task duration, starting date, and end date. Moreover, I need the task ID to be randomly generated.