“Sir, are you ready to check out?”
You work at a hotel. A guest who's been staying at the hotel has all of his luggage. You say this as he walks toward the reception desk.
Sir, are you ready to check out?
Employees who deal with the public, like cashiers, receptionists, security guards, hotel staff, etc. often call male customers "Sir". It's supposed to show respect. For example:
Sir, can I get you something to drink while you wait?
In the U.S., you can also call any adult man who you don't know "Sir".
Excuse me, sir. I think you dropped this.
The equivalent title for women is "Ma'am".
Ask this question to find out whether someone is prepared to do something and whether they can start doing it.
Are you ready to go?
Are you ready to begin?
You can also use "Are you ready for ___?"
Are you ready for school?
Are you ready for dinner?
When you stay at a hotel, you "check in" when you arrive. When you leave, you have to "check out". This means letting the hotel staff know that you're leaving, returning your room key, and paying for the room and any extra expenses.
The preposition that follows "check out" is "of":
A: Let's get going!
B: Hold on. I have to check out of the hotel first.