Since searching in Windows 8 has changed significantly, here is how you can use the search feature in almost any app in Windows 8.
(A) Using the Mouse
(1) Move your mouse to the bottom right-hand corner of your screen, or press the Windows + C combination to bring up the Charms bar, then go ahead and click on the SearchCharm.
(2) On the right hand side you will be given a list of apps that support searching in one way or another, select the app you wish to search.
(3) If you look at the top of the sidebar you will notice that the search context will have changed to the app you selected. Go ahead and type something in the search box and press enter.
(4) On the left-hand side you will see your app open and display the results of your query.
(B) Using the Keyboard
If you would rather use the keyboard you could press the Win + F keyboard combination and go straight to the search screen.