I'm having a colonoscopy tomorrow too! This is not my first one, though. I've had a few over the years. They're not bad. Today you (and I) are doing the prep - no eating, which sucks. You have to empty your bowels - I'm taking Miralax, but I'm not sure what you're doing. Probably something similar.
For the test, you'll go in to the hospital, check-in and do some waiting. They'll have you change into a hospital gown (which I hate, but oh well) and they'll start an IV. The doctor and the anesthesiologist usually come greet you. You'll then be taken back, when they're ready for you, and you'll be given anesthesia. When you wake up, it'll be done!
Afterwards you may feel bloated and/or your throat might feel a little funny, depending on where they stick the tube. This passes, though. Once you're awake enough and they make sure you're feeling well, plus they take the IV out, you can leave. You can't drive though!
I may have left some little things out, but these are the main steps. The actual procedure is only around 45 minutes or so on average. The nurse told me that I should be out of the hospital in 3 hours, so hopefully it'll be similar for you.
I hope this helps! Even though I've had lots of tests over the years, I still always get a little nervous. But it should be fine!