Wallpaper app for android possible?

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Visual-Studio

Android

Xamarin

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Okay so the title might be incorrect.

Im 100% that it is possible to create a wallpaper app for android.
Anyways..

Im starting off my first app for android and I though to myself, what can be fun to create? An wallpaper app that seems like it would be easy (from past experiences with C# and the .NET Framework)

But now I want to create one for android as I stated earlier.
Basically I want the app to work like this.

You start it (Duh)
you get prompted with a few random pictures
you have a search bar where you can search for anything lets say "Cats" (Im pretty sure I need to hook up an API for that, will probably use google's)
you get prompted with a bunch of pictures of cats
you can save a picture to the phone

Super simple right? The only thing is
I dont know where to begin, I know the fundementals of app development for android but creating something like that..

If anyone could share any links or tips that would be amazing!

What I have tried:

Googleing for answers and tips and trying to find tutorials