Find device task manager screen?

There is a taskbar (there isn't a task manager as you would find on a computer) which shows recently used active apps - double-click the home button and it should appear at the bottom of the screen.

To close an app via the taskbar, then press and hold any of the apps on it for a couple of seconds or so until they start shaking, then press the '-' in the top left of an to close it, and touch any part of the screen above the taskbar so as to stop the shaking and close the taskbar.

If you haven't got a copy then you can download a copy of the iPad manual from here : http://support.apple.com/manuals/ipad/ - it has a short chapter on each of the built-in apps (plus iBooks which is a free download from the store), plus some general info about the iPad