The "Main" screen is what you use when shooting. As you type in different conditions at the top, the numbers at the bottom change immediately
The "Options" screen sets up your rifle and ammo. The paid version has a Bullet and Ammo database, and you can save your own loads
The "Setup" screen sets up your preferences, and what the weather is like.
The "Sim Setup" screen sets up random scenarios for traing purposes.
The "Sim Graphics" screen sets up the Graphics for the target and background. Use images from your Android!