Multi-window opens up a lot of new possibilities, but designing for split-screen multi-window starts with a responsive UI (see our previous video on building a responsive UI: https://goo.gl/mcjKYK). With a few special considerations for the 16:9 layout for mobile devices in portrait and the 34.15% tablet layout, you’ll have a great looking app.
Just know that multi-window is enabled by default - test thoroughly, particularly for exported activities that should always support multi-window.
Read the full documentation for the details and what APIs are available: https://goo.gl/2myNde
Then check out the sample and try it for yourself: https://goo.gl/lfBcgI