The Search charm
Here's where you search for apps, files and settings. Just click the appropriate item in the pane on the right and type the first few letters of your search term; the results will appear on the left side of the screen. You can also search inside any app (such as searching for emails in Mail) by selecting it in the right pane and typing a few letters.
To start a search from the Start screen, you don't have to manually launch the Search charm. Just start typing, and the Search charm appears with your text in the search box.