If you want to show a specific image in a Xamarin.Forms app based on a condition, you can Image.Triggers
For example you have an Image element in your XAML and you want to show a different image based on a database query. In order to do that, you should place the pictures that you want to use in the appropriate folders.
For iOS the pictures must be located under Resources folder.
For Android the pictures should be in Resources/drawable
For UWP you must place the pictures in the root directory of the project.
Ever wondered how to create a Bottom Navigation Bar for Xamarin.Forms as it is in the latest Android sdk version? As there is no native control for Xamarin.Forms you could create a custom one with a Control.
First create a Folder and name it Controls and create the control in there.
In your portable class library -> Add New Item -> Content View and name it NavigationBar or something else.