I) In development fields everyone prefer CROSS PLATFORM application and Xamarin fits in it.
II)It is a free open-source framework to build truly native cross-platform mobile apps using C# .NET for iOS, Android or Windows.
III) Xamarine runs on .NET and Mono to build app.
IV) Xamarin allows you to develop native apps using C# language and platform-specific tools/SDKs and share the same code across multiple platforms - iOS, Android or Windows.
Q2) Which approach provided by Xamarin?
A) Xamarin Native
B) Xamarin Form
YOU HAVE SELECT THIS RIGHT BEFORE START THE PROJECT. Because it is difficult to change later.
For example, in IOS& Andoird ACTION behaves differently.
II) If you wish to keep the system behavior as it is than use xamarin native.
Q3) What is Mono?
It is free open-source .NET framework developed by Novell and owned by Xamarin.
The main purpose of Mono project is to run .NET based applications on cross-platform including Linux, Android, Mac etc.
Q4) What is difference between FORMS And Native?
I) If you used the native then you have code for
Xamarin Android Xamarin IOS so on.
That means NATIVE have multiple Code base.
II) While if you select FORMS then you have only one CODE base
AND at the run time it will generate different build for
Android and IOS so on.