In Mandarin, it's xie xie. You would use it when anyone shows hospitality or gives you something. If someone picks up some food and brings it to your plate you would say xie xie but if someone poured tea for you, you would lightly tap your index and middle finger together on the table. This gesture originated in the old Chinese practice of "koutou". This is a very traditional gesture that is when someone gets on their knees and bows their head, the higher place the person, the lower your head goes. This gesture is rarely practiced nowadays but according to legend, one day, the Emperor decided to wander into the public to enjoy a lunch. He was sitting at his table with his advisors when he suddenly picked up the teapot and poured tea for them. His advisors were shocked and didn't know how to respond. Normally, they would koutou, but it is inappropiate for one to leave the table without completion of a meal ESPECIALLY leaving the Emperor. So they rapped their fingers on the table to symbolize their legs on the ground bowing to him.
In Cantonese, there is two ways to say thank you. One is "daw jhe" and it is the more casual one. Because saying thanks is to show one's gratitude and respect, it is not used as often. It is usually used when one is paid a compliment or given something casual. Usually, you would say "daw jhe" when you receive something that the giver is not obligated to give. Often, you would rarely use this to thank an elder.The other saying is "mm goy" and this is the more respectful and proper way to say thank you and thus is used more often. It's used for when you are given almost anything and the best way to thank an elder.
