Between Xamarin forms and Android Studio, which is better for noob/beginner like me.

Answer 1

See this table:

https://i.imgur.com/hMHMEUT.png

Answer 2

Since you are a beginner i would say try xamarin first as it will allow you to build a mobile app with c# and Xaml for the UI markup that will run on android , IOS and Windows as a UWP or store app with the same code. Even the UI code is shared so this can reduce the learning curve and reduce development time as well as teach you a general purpose language and libraries that you can use even for desktop web and other types of apps.