Hi Rose,
Your friend is talking about 'Advance Passenger Information'. It is where you supply your date of birth and passport details to the airline.
On many of our holidays, this is completed by Just You with the information that you have provided us with when we check the group in. On some occasions, this is something that you would need to do yourself - information on how to do this would be supplied in your final documents. Should you be asked to complete this, it is a very simple process - you visit the airlines website and go to a 'Manage your booking' section (you would be given some details to log-in with) and you complete the required fields.
I hope this information helps,
kindest regards,
Julia