OS X offers different tools for working with multiple applications and windows, allowing you to switch apps by clicking icons in the Dock, or by pressing Command-Tab and using the Application Switcher. But if you work with more than two or three apps, you may find that your display becomes messy. I generally have at least a half-dozen applications open at any time, and having all those windows on my display can make things confusing.
Fortunately, El Capitan lets you use Spaces, or virtual desktops, to organize your windows, and keep your apps from becoming unwieldy. Spaces are part of Mission Control, a built-in feature that lets you glance at every currently open app and window on your computer. You can access Mission Control in several ways:
Read more here:: Hands-on with Spaces, Mission Control, and Split View in El Capitan