The most obvious change in Lollipop is the fresh design aesthetic, called Material Design. It uses a lot of bright, rich colors and adds depth with shadows to give Android a sleeker, more minimal look.
If you want to take a break from your endless app notifications, but still want to hear from important people, there's a new mode called Priority. You turn it on from the volume controls and it blocks any less important alerts.
Another new feature in Android 5.0 is screen pinning, which means you can lock an app on the screen so that the user can't exit it. It's useful if you loan your device to kids, so that they can only play a game and not mess with your Facebook account.