Hello everyone,
I am new in developing mobile applications. I am trying to start a simple project on Android/iOS/Windows phones. The application should contain a login page that the user enters username and password and the application should check these info on the local SQL server and check whether the user is registered or not. I have couple of questions and just need your help 
1) How to create the server tasks (PHP, Json...etc) and what should the server send to the application?
2) How to connect the xamarin.form project to that SQL server to check the info the user entered?
your help will be really appreciated
Thank you in advance!