When working in apps on documents you can choose to have one document open per window, or multiple documents in tabs in that same window. Windows can be floating, resizable objects on your desktop, or you can go into full screen mode to fill the screen with the window or split screen mode to share the screen with exactly two app windows. You can also combine windows, tabs, and screen modes to work in many different ways.
Split View allows you to use Full Screen mode but with two apps instead of just one. You start Split View by holding the green button on one window and then choosing the left or right side. Then you click on another app to place it on the other side. The Split View screen acts as a Desktop and can be accessed from Mission Control. You can exit Split View by using the green button again on one of the two apps, which leaves the other app behind in Full Screen mode. But there is a way to exit Split View and return both apps to normal mode at the same time.
Mission Control in macOS Sierra allows you to create multiple desktops with different windows on each. You can easily create these desktops and move between them with keyboard shortcuts. This allows you to go between apps and workspaces easily, saving you time and effort. You can also use full-screen apps as a desktop. This is handy for MacBook users in particular as screen space is limited.
If you use Mission Control, you can assign an app to a specific desktop so when you launch it it automatically appears on that desktop instead of the current desktop. You can also assign an app to appear on all desktops, which is handy for note-taking and other tasks.
Split View is an underused viewing mode where you have exactly two apps on your Mac's screen at once. It is similar to Full Screen mode and works in conjunction with Mission Control.
Get to know the new Lion gestures. You can use a trackpad on a recent MacBook or a Magic Trackpad to navigate around in Mac OS X 10.7 Lion. You can also do some gestures with a Magic Mouse. See where to enable and customize gestures.