Q: what is 3G and how do I use and set up for my ipad2?

3g is having access to internet when wifi is not present. you can be on the road and check facebook.go to settings>cellular and have it on.

no you dont need one follow steps below

for at&t

http://support.apple.com/kb/HT4157

for verizon

http://support.apple.com/kb/HT4571

of course if you purchased an ipad wifi you CANT GET 3G YOU HAVE TO PURCHASE IPAD 2 + 3G

if it came with one put it in. usually it already installed