You will not feel any output coming out at all! Do you feel poop going through your intestines? It's the same thing!
At first the bag is a lot to deal with, but it's not terrible! If the looks of it bugs you at all (meaning the stool, because with the appliance on, you won't be able to see anything really!) you can wear opaque bags that won't allow you to see anything at all!
Good luck with everything...if you need someone to talk to, I'm more than happy to help. I'm 21 now and got my ilestomy when I was 19. You will get through this!
PS: As lots have mentioned, come over to the ostomy forum. We're all great there and it will provide you a wealth of information. I actually learned more from the forum, than I have from nurses and doctors!