When you select the Controls tab in the Options Menu, you can turn the Invert Y-Axis, Pinch To Zoom, and Vibration features on or off by tapping the circled icon on the right of the respective option. If a green tick is shown, it means that the feature is on. The Aiming Sensitivity feature can be altered by holding your finger on the slider and moving it left or right.
Turning Invert Y-Axis on will mean that the direction the camera goes when aiming in missions will be flipped by the vertical axis (e.g. swiping your finger upwards will move the camera downwards).
Turning Pinch To Zoom on will mean that you can do a pinching motion with your fingers on the screen to zoom in with the scope during missions.
Turning Vibration on will allow your device to vibrate at various points in the game (this feature is not available for all devices).
Changing the Aiming Sensitivity feature will determine how quickly the camera will move when you aim during missions. Having this bar to the left will provide slow movement whereas having it to the right will make the camera move quickly.