Guangdong, Guangzhou to Kouloun?

You must refer to Kowloon in HK, right?
In the Lianhuashan Ferry Terminal, you can take the ferry to China Ferry Terminal (in Kowloon area) directly. The ferry is scheduled at 08:30, 10:30, 15:20 and 17:20. There is no English website for booking, you can turn to your hotel with the reservation.

In Nansha Ferry Terminal, there is a ferry at 09:30 to the HK airport directly, and the duration is about 60 mins. It is a closed channel only served for the passengers who are going to take a flight from HK airport. So you need to book the air tickets in advance, otherwise, you cannot use the ferry to the airport.
You can book the ferry tickets on the official website of Turbojet. It has an English version, you will have no trouble with the booking on your own.