If you're a Google fan, Apple's new Spotlight feature will look very familiar. It launches as a thin search box right in the middle of your screen. Start typing, and OS X Yosemite will start auto-suggesting all kinds of things: messages and email, locations on the Web, and more.
The idea is that Spotlight lets you start searching without first having to open and hunt through a particular app. Spotlight can be used to open applications, contacts, calendar, mail, messages, a dictionary, and even system preferences.