Camera View like airplane shooting game

I’m trying to develop a game for Android in 2d like [Youtube Videos][1] but i’m facing a lot of problems.
I’m trying to create the camera view and lock the player inside it. I already have a lock system so that the player can’t go outside of a box, my question now is how to make the box and the camera that use all the space of the phone display.
Actually, i have created a level and placed the player ship as 2d image that you can control, but i don’t know if this is how you should develop a game like this. I remember in unity i didn’t create any level, i just used the UI and placed the player directly inside the UI and so everything was done in automatically. Should i do the same thing there or create the level and place there the user ship etc is the correct way to develop such a game?
If that so, how can i be sure that every thing that i place in this level will be equal on all the phone displays?

I hope i make myself clear, i’m not english