Every Android user has a theme on their phone. They just don't know it yet.
It's true. Even if you don't know what icon packs or launchers are, if your phone has a home screen on it, it's got a theme. Android users don't have to live in their app drawers: they can choose how their phone looks and functions. They can use widgets to interact with apps without opening them. They can use custom icons to theme or obscure the apps on their phone from prying eyes. They can even use gestures and contextual data to help their phone adapt to where they are and what they're doing.
So, what are Android themes and how can you get started with one?