As far as I know it just means that's (3g) the network you're connected to. So if you were to surf the net on your phone you would get 3g speeds (speed might vary depending on several factors). I occasionally get an "H" which is the HSPA network here in Canada. It doesn't necessarily mean that you're surfing the net and using data. Just make sure that there's nothing in the background using it (ie. I have a version of MSN on my cell phone. When its active its up on the top left corner. That means its using data in the background to stay connected.)
If you push and hold the little house key (home) a window should pop up showing the last six apps you've accessed (internet, settings, messaging, etc.).
If you push and hold the hang up button you can silence the phone, turn on airplane mode or turn it off.
Ummm I'm not sure what else. The back button will take you back one webpage when you're surfing the net. It'll take you back one step with just about anything else. Doesn't delete text if you're texting though.