Apple long ago perfected system search on their computers and laptops with a system called Spotlight. Spotlight is quickly accessible and searches automatically for documents, settings, applications and other items and displays the results as you type. It is so good that Microsoft started copying the feature in Windows Vista and came close to duplicating it in Windows 7 and 8.
Anyway, I digress. Apple brought that great search to their mobile devices and operating system and it is equally useful and quick. To access Spotlight on your mobile device, you can either push your home button once, pause and then push it again OR you can swipe all the way to left most screen. When the Spotlight search screen appears, the keyboard automatically appears as well and you can start typing the first few characters of an app (VERY helpful if you have many, many apps and screens), a contact, a reminder, a song, a calendar item or many other pieces of information on your device. It makes navigating your iPhone or iPad MUCH faster.
Watch the short video below to see a couple of examples of how to use Spotlight search and how to customize the results just for you.