Letterheads for business

To apply for a business account it says i will need to bring in a letterhead for my business.
What should a letterhead include? as my company doesnt have a phone number. I just use email and a PO box.

Also as ive just started i havent registered my business yet as i havent earnt anything from it yet, will i need to register it before i get a bank account or can i do that after?

Thanks