If your iPad is running iOS 5 (I am not sure if these apply to earlier versions)...
Screenshot: to take a screenshot, press Power and Home buttons at the same time; the screenshot is saved in Photos.
Folders: to create a folder, tap and hold on an icon until all icons start to jiggle, then drag one icon over another and drop it. A folder is created with both icons. You can rename the folder: get all icons jiggling, tap the folder icon, then tap the folder name -- a keyboard pops up to edit folder name.
View all running apps: double-tap Home button.
USB charging: iPad needs a high-power USB connection; many USB ports on laptops, desktops and USB hubs are low-power. The iPad might charge even on the low-power port, but it will take a long time and the iPad must be turned off.
