I'm a newbie here and haven't quite figured out what the term ARC means.  What is it? 

It is an "Advanced Reader Copy."  It is released before the actual book is released for people to review, edit and promote.

How would I be able to tell if I have an ARC?  Are the covers and prints visably different?

Tamara,

Sometimes an ARC will look just like the final book and will usually have the same IBSN as the final book.  An ARC  is usually (maybe always)  softcover and will say something like "Review Copy," " Uncorrected Proof," "Not For Sale" somewhere on the book. 

Actually it is an Advance reader copy (not advanced, they are anything but)

Always check inside the book, all have to state somewhere that this is an uncorrected proof and not for sale. Plus it will also state the publishing date, usually on the back where the barcode is or should be, it should read "Not for sale".

I've yet to come across a hardcover ARC, but most now days have the same or similar cover to the published title.

Art work can be missing, author dedication might read "Yet to come" and other things can be changed or missing. Spelling mistakes, bad grammar and character names can also be different from the published copy so please dont send these out unless the requester is asking for it via the book bizaar.

An ARC is not the same as the real published book.