I am new to Xamarin. I have few confusion here.
Question:
I think you are way off.
Xamarin provides C# and the .Net (Mono) runtime on iOS and Android. At the same time they expose the native APIs on each platform to C#. So they built a way for C# to call into Objective-C and Java (and vice versa).
This means you develop native UIs on each platform, and can share backend business logic between platforms. A Xamarin app can share somewhere between 50-75% of its code across platforms. There is no general sharing of the UI across platforms, since this would abstract away the native APIs.
To break it down:
Android
iOS
Both options you can create your UI from code as well, but the native APIs will be different on each platform.
*A mac is needed to compile for iOS