On getting fired... It's usually an unplanned meeting shortly after you get in, possibly with HR present. Take a deep breath, and realize the decision has been made, and no amount of explanations, excuses, circumstances, or bargaining will change it. Keep your mouth shut. Don't bother asking them why; they won't say, and then you'll start guessing. There's nothing you can say that will help you. Don't sign anything; say you'll take home whatever documents they give you to review. Don't help them pick up your work where you left off--you don't work there, they made it clear they have no interest in you working there. Take all your personal belongings, return theirs. If they let you send a farewell email, send something generic (or not at all). As always HR is not your friend.
In short, keep every interaction as curt as respectfully possible. It minimizes professional impact, and if something leads you to legal action, it puts you in the best position for it.