Visa to travel

I am a UK resident going to visit a friend in china (german student, currently studying in Beijing), I have read about needing a letter from the invitee what information is needed in this (if it is needed) and we plan to travel whilst in china and are unsure of what to put in the residences box as I have no hotel reservations and will be backpacking (staying in hostels) or staying with her friends on the trip, but do not know where yet. Do I also have to have a copy of flight bookings with me at the time of application?

Thanks