welcome to ft

i think there is a FAQ that covers it that is one of the threads that is stickied:
http://www.flyertalk.com/forum/unite...lines-faq.html
and just scroll down to the upgrade related threads

basically, systemwide upgrades should only be used for non-domestic UA flights if you have confirmed regional upgrades. the systemwides upgrade internationally and domestically and confirmed regionals only upgrade domestically. systemwides are the only way to upgrade internationally i believe (except maybe like upgrade for cash when you check in), or using miles. but you have to pay a little more to be able to upgrade the flight-someone with experience flying international could maybe give some more detail.

confirmed regional can be used for domestic travel on UA metal. you can confirm in advance (as early as time of booking) a first class seat.

the e-500s can also be used on UA metal, but they only confirm 100 hours before the flight for 1Ks. so if you really want your first seat on a flight, a confirmed regional is the way to go. also, you should use up all your e-500s because sometime in quarter 2 they will become worthless with the new unlimited domestic upgrades.

those are the basics, its all been talked about in other threads, and the faq points to a very helpful thread that talks about e500s. you should definitely get familiar with those threads-as they offer a much more in depth look at how the upgrades work