The Start screen replaces the Start menu in Windows 8 and Windows RT.
Open Start by swiping in from the right edge of the screen (or if you're using a mouse, pointing to the upper-right corner of the screen and moving the mouse pointer down), and then tapping or clicking Start.
You can pin apps, contacts, and websites to Start to easily access what you use most. All of your apps — both apps you install from the Windows Store and desktop apps—are available from the Start screen. You can organize, group, and name categories of apps in whatever way makes sense to you. For more info, see Customize the Start screen.
If you're on the Start screen, you can use the Start charm to go back to the last app you were in. For more info about charms, see Search, share, change settings, and more.