Spotlight is a lovely little search feature built into Mac OS X which you can find in the top right corner of your screen. It looks like a magnifying glass which, when clicked, presents a search box. You can type in this search box and your Mac will search everywhere, including within your email and documents if you prefer, to find what you are looking for.
A very quick way to find and open an App on your Mac is to simple use the shortcut key to open Spotlight (hold the CMD key and press the Spacebar at the same time), then type the name of the app (or part of the name) into the search bar. The app should appear as one of the first search results, which you then simply click in order to open it.
If Spotlight does not find the Application you were looking for, it's probably because you need to include Applications in the search results. To do that, or to configure spotlight searches in general, go to the Apple Menu which is located in the top left corner of your screen, select System Preferences and then click the Spotlight icon. You will be presented with a list of all the things that you can have spotlight search, or not, as the case may be.