how to connect asp.net and android app

Here we have two applications (Asp.net & Android) and one central database(same database for web and mobile app). Asp.net application will provide you the services(either web services/wcf/rest ful) to insert/update/delete/Select data from database. from your android appliction you can consume that services to perform operations like insert/update/delete/select.

Assume if your android app wants to do some operations(insert/update/delete/select) in offline mode(i.e. no internet connection) the you can create your local database( using SQL lite) and stor the data in your local and whenever internet is available sync your local data with Server database (these synching process has to do automatically).

First analyse your app requirement, is your data should sync with server database or not.

I hope it will give some idea to your query, If youlike my answer please accept it.