What do you want to do and where do you want to go? Are you in Thailand right now and do you want to book a domestic flight? For example, from the airport closest to your hotel to cities (Bangkok, Ayutthaya, Chiangrai, Chiang Mai, Phitsanulok, Kanchanaburi, Pattaya) or island (Phuket)?
Click on "Domestic flights".
Do you want to travel from Thailand to other countries in Asian (e.g. Singapore, Malaysia, Hong Kong), click on "International flights".