What do you want to do and where do you want to go? Are you in mainland China right now and do you want to book a domestic flight? For example, from the airport closest to your hotel to cities (Shanghai, Beijing, Xi'an), province (Guangdong, Fujian) or island (Hainan)?
Click on "Domestic flights".
Do you want to travel from China to elsewhere (e.g. Singapore, Thailand), click on "International flights".