How do I bite with a jaw allignment appliance?

I just got a jaw alligment appliance put in today. Its called the Herbst device from the Damon System Orthodontics. I think I'm only supposed to have it for around 3 weeks but the website say 8 to 10,but anyway, I was wondering, how am I supposed to bite down with this thing? I know its supposed to move the lower jaw forward but I can't bite down without nearly breaking my jaw! Does it just get some getting used to or is there something I can be doing? Eating isn't too bad, its just hard right now...any help is appriciated:)