Mac OS X uses a program called Spotlight to search your computer and the internet for files, emails, word definitions, websites, etc.

There are two quick ways to access Spotlight.

Method 1: Click on the magnifying glass in the upper right-hand corner of your screen. 

Method 2: Use the keyboard combination Command + Space.

Either method will bring up the Spotlight search window, which looks like one of the two images below, depending on which version of Mac OS X is on your computer.

If you are using Mac OS X 10.9, Mavericks, or earlier the Spotlight window will look like this.

If you are using Mac OS X 10.10, Yosemite, or later, the Spotlight window will look like this.

When the Spotlight window is open, simply start typing in the name of the item you wish to find.  Spotlight begins searching as soon as you begin typing, and it is not necessary to type in the exact item name.

Search results will look like one of the two images below, depending on which version of Mac OS X is on your computer.

 If you are using Mac OS X 10.9, Mavericks, or earlier the Spotlight search result will look like this.

If you are using Mac OS X 10.10, Yosemite, or later, the Spotlight search result will look like this.

As you can see, Spotlight searches for many different things, including: your user files, your emails, dictionary definitions, Wikipedia, the internet, and more.  Spotlight is a very useful tool that is easy to access and use for finding things on a Mac computer.