Spotlight lets you search your Mac making it easy to find whatever you need. It indexes the contents of your Mac's hard drive to make it easier to find documents, emails, apps, music, contacts, and other information. It can also help you find information on the web, and perform equations.
Click on the Spotlight magnifying glass icon in the menu bar, or use the Command-Space keyboard shortcut. The Spotlight search field will appear in the middle of your screen.