The case probably came with a plate in the back already for all the I/O ports. Simply give it a little push, or a big one from the outside, and it should pop right out. Your motherboard should come with it's own little special plate that should fit perfectly. Just make sure when you replace it that you put it in right-side-up. I've put it in up-side-down numerous times
Yes! You're right. It DID come with a plate on the back already, and I found the replacement plate. Thanks man. As you can probably tell, I'm a first time builder, lol. And I'll try and remember the upside-down thing, lol.