I'm not sure if there's difference (looks up on wiki answers.)
hmm, I'm not sure if I can give an accurate definition of that. They seem pretty much the same except an expo seems bigger....much bigger.
I would like to say something about panels though. There are voice actor panels where voice actors are asked questions by the fans. I highly recommend that you go to your con's website (yes, most cons do have a website) and check out to see what voice actors they will be hosting. Why? Because a fav. VA of yours may be there, and you may want them to sign something for you. I also recommend avoiding what are called "uncensored panels". It means what it says, it can be explicit. I've never been to one, but I've heard of them.
ALSO! Avoid bootlegs. What are bootlegs? Fake copies of a product. This happens with not only DVDs and manga-scans, but with other things like plushies as well. I once bought a plushie Mokona, but it turned out to be a fake cause I looked at the real product online....it didn't match up, plus it had no "sown-in tag" like plushies should have. I don't know about you, but I certainly don't want a fake, low quality item.
Plus, none of the money goes to the artists or creators when anyone buys a bootleg, so no one wins.
....But, thankfully there are ways to tell if something is a bootleg or not. It's a bit long to type out, so feel free to let me know via PM if you have any questions about this.
Anyway, I hope I was of help to you.
! And may you have lotsa' fun at your 1st con! XD!