what is the "the HK Post General"?

Thanks very much.
what does it mean "the HK Post General". Is it a place where I can go to pick my passport? I prefer to pick it by myself.
Is the bank to pay the application fee close to the consulate?
向我這樣沒有香港居留的人，算第三國簽證吧，Do I need a letter from a Hong Kong institution to certify that I travel to HK for business?
Thanks very much.