confusion between Unity and Unity android

Im just a beginner, and once i code my game, i go to build settings and then just build and run my game on Android.
Is this a wrong way to do, or is there something called Unity android that is different from “unity”?
If unity android is different, where can i get that?

There is only one Unity, from which you can build to PC, Mac, Android, iOS, Blackberry, PS3, XBox, PSVita, Unix… just by changing the “target platform” setting. Neat, huh?