Spotlight is probably one of the most underused features on your Mac, but it is a pretty powerful tool. Located in the top right corner of your screen, the magnifying glass is often overlooked. Clicking on it gives you the ability to search your computer for programs, documents, pictures, and that email you know you received, but can't seem to find anywhere. It's basically Google for your Mac! Search by word, name, file type, whatever. Then preview the item to make sure it is what you were looking for before you open it. It's a great way to quickly launch a program on your Mac. You can even use Spotlight as a calculator or a dictionary. Check out the video below to see it in action.
Apple support has more information on Spotlight here.