WINKEY – Open/close the Start Screen.
WINKEY + C – Open the Charms menu, which gives you options for Search, Share, Start, Devices, and Settings.
WINKEY + D – Switch to the classic Windows Desktop.
WINKEY + F – Search for Files via the Search charm.
WINKEY + I – Opens the Settings pane, which gives you current app settings, along with options for Network, Volume, Brightness, Notifications, Power, and the ability to change more PC settings.
WINKEY + L – Locks your PC and returns you to the lock screen.
WINKEY + O – Changes screen orientation (portrait/landscape) for tablet/slate PCs.
WINKEY + P – Opens the Second Screen panel so that you can choose how content on a projector or additional screen is displayed.
WINKEY + Q – Search within Apps via the Search charm.
WINKEY + Z – Opens the App Bar in a Windows Store app.

Also, when at the Start Screen, you can start searching for apps and programs just by typing. When searching, you can always change your search context (Apps, Files, Settings, search within apps) by clicking or tapping on the name of the item on the right-hand side.