Hi there. I need to book a train from Cambridge to Broxbourne. 
Is there a day you need to leave? Do you have a time you need to leave or arrive? 
I'm sorry, I actually need to travel from Broxbourne to Cambridge.   And yes, I actually do need to leave after 13:00 on Tuesday.
All right, the TR8199 train leaves at 13:32 on Tuesday. Would you like me to purchase tickets for you?
Yes, that would be great.  I need 8 seats.
Alright, I have your 8 tickets purchased for the TR8199 train. Your reference number is ZJ8KWJQ9. Is there anything else I can help you with?
No, that's all I need.  Thanks.
You're welcome. Have a nice day.