how do you take the back off to insert sim card, how do you take the back off to insert sim card

With an iPhone you don't need to take the back cover off (attempting to do so may damage the device). Instead look around the edges of the iPhone for the SIM tray. On an iPhone 4 the tray is located on the right hand side of the device, and on all other models it is on the top edge. Simply insert the end of a paperclip into the hole on the SIM tray and push gently.

Here, this might make things a bit more obvious (taken from Apple's iPhone user guide).