Congratulations. 🙂
You can use it, that's fine. Once it's charged you should unplug it and wait until it completely runs out of battery before plugging it back in again. It'll give you a warning that it's about to start using reserve power about five minutes before it falls asleep. It's important to not plug it in before that though. Throughout all of this you can use it though. 🙂
iGary, I think you're meant to charge it first, then run it from the battery.