The iPad has built-in wi-fi. In terms of a sim-card, if you bought the 3G version (and it's not the Verizon model) then there should be a sim-card slot on the left-hand side of the iPad : http://support.apple.com/kb/HT5163
The sim card is not used for wifi. It's used for 3/4G cellular.
Complete guide to using iOS 6
Guide to Built-In Apps on iOS
You can download a complete iOS 5 iPad User Guide and iOS 6 iPad User Guide here: http://support.apple.com/manuals/ipad/
Also, Good Instructions http://www.tcgeeks.com/how-to-use-ipad-2/
Apple - iPad - Guided Tours
Apple iPad Guided Tours - Watch the videos see all the amazing iPad apps in action. Learn how to use FaceTime, Mail, Safari, Videos, Maps, iBooks, App Store, and more.
How to - Articles & User Guides & Tutorials
iPad How-Tos http://ipod.about.com/lr/ipad_how-tos/903396/1/
You can download this guide to your iPad.
iPad User Guide for iOS 5