Talking [Q] Use only part of the screen

Hey, is there a way to use only part of the screen in an android? Most of the time, the screen is the biggest cause of battery drain, so I am wondering if I can use just part of the screen. For example, can I use only the top half of the screen with the bottom half either displaying black or turned off? I'm pretty new so I'll probably need step-by-step detailed instruction. My phone is a galaxy s3. Thanks if anyone can help