Oh My. Welcome to MobileRead. You certainly don't have to have it registered to use, but to access Amazon books you will. You can either go to the Amazon site itself with your PC and register by using the serial number or you can do it directly from the Kindle under settings (I believe).
The 5-way control is quite simple just a joystick up to move the highlight up, down, etc press it down to select the highlighted item.
To transfer books from the computer to the Kindle. I think you will have to download them again but specifically for the Kindle itself rather than for the Kindle4PC (though I'm far from certain about that)
I'm sure the duck
(daffy4U) will be along who is a kindle expert.
Also on the Amazon site are Kindle forums and help and people and information..