I have never had to fill in a reference number for a Direct Debit, anything like that would always (in my memory) have been pre-populated by the company who wants my money. But the only logical thing I can think is that the company has provided a blank form where you have to fill in all the fields. In this case your Reference must be something so that they can link the Direct Debit to your account with the company (note italics: I am not referring to your current account number). This must be something provided by the company on a bill or suchlike.
If you are unsure of what to put in the Reference field, contact the company in question. Make sure you get it right or they won't be able to take any money, and you will go into debt with them for unpaid bills.
By Address, I assume it is clear on the form that they want your bank's address? (It's not clear from your question). In that case, Address would normally be the branch address.