Lifecycle methods are to be used to run code and interact with your component at different points in the components life. These methods are based around a component Mounting, Updating, and Unmounting.
Xamarin.Android application lifecycle is the same as normal Android app. When talking about lifecycle we need to talk about: Application lifecycle, Activity lifecycle and Fragment lifecycle.
In the below I'll try to provide a good description and way of using them. I obtained this documentation from the official Android and Xamarin documentation and many helpful web resources provided in remarks section below.