Multi-screen is for watching more than one channel at the same time. Only one channel will have audio but you can toggle back and forth to which channel is playing audio. The more channels you are displaying at the same time, the more resources are being used and the more bandwidth is needed. Normally with 2 - 3 screens you'll be fine, but as you add more you'll eventually start to get buffering and possibly not work at all.
Picture in Picture is not the same as multi-screen, it is only shows what you are currently watching on a small screen on the bottom right of your screen and returns you to your home page. You'll be able to scroll and click through your home page, but if you try to play something, the Picture in Picture will quit playing.
To use either, when on a channel, press the selection button to bring up the menu on the bottom, then go to either Picture in Picture or Multi-Screen and select and follow the on screen instructions. Picture in Picture is only good if you need to return to your Home Screen.
