For questions concerning the icons on the notification bar, which usually sits on top (phones) or bottom (tablets) of your device's screen.

Notification icons appear in the notification bar, which usually is located at the top (phones) or bottom (tablets) of your device's screen:

Notification bar Notification bar (Gingerbread)

They stand for information (e.g. new mail, like the 2nd icon in the screenshots), ongoing events (3rd icon: USB connected), warnings, running services (all those usually on the left-hand side), or states (usually on the right-hand side) like WiFi/cell signal strength, battery, and time.

Example questions you might be interested in: