Sniper Shooter puts you on a rooftop with a scope and a strictly limited number of bullets: identify the target, line up the shot, and take it cleanly.
The ammunition limit is what makes it a game. With unlimited bullets it'd be a shooting gallery; with three, every shot is a decision.
Each mission gives you a strictly limited number of bullets, which turns a shooting gallery into a decision about when to take the shot.
Zoom in fully and wait for the target to be stationary. Leading a moving figure through a scope is far less reliable than waiting a moment.
Yes — tap and drag to aim, release to shoot. Nothing to install.