New to Unity 5, I'm interested in android game making

Hey guys, So I watched a tutorial in Lynda.com and made a 2D game that I believe was supposed to fit in all screen resolutions. However when I installed the game into my android phone I could only see half of what I could see in Unity's game preview window (when the platform was set to PC) So I was just wondering how easy it is to make an android game fit all screen resolutions? If not all, most.

Also any tips would be great! If you know any tutorials to 2d android game making, I would appreciate it if you shared them :)

Do you guys start a project by setting up the background? and then camera? What's some essential things to do when you begin a project?

Sorry for the many questions. All responses are appreciated!