It should be through their application website, the one that they linked you to right after they received your application. They will also send you a packet via snailmail, which is roughly... 3 days after releasing online.
they should. some of the school i applied to have already announced theres. "Applicants will receive notification via email of the exact time that decisions will be posted. You will need to login to your Duke account to access the decision." thats from the duke admissions website. they send out an email about when decisions are gonna come out. rumor has it the monday before the 1st though. we'll just have to wait and see.