Thai often adds a little word at the end of a sentence to make it sound polite. The choice depends on who is speaking, not who is listening.
Men: ครับ (khráp)
Men commonly use ครับ with both statements and questions. The same ending works whether they are speaking to a man or a woman.
สวัสดีครับ
Hello.
สบายดีไหมครับ
How are you?
Women: ค่ะ (khâ) and คะ (khá)
Women commonly use ค่ะ for statements and replies, and คะ for straightforward questions.
สวัสดีค่ะ
Hello.
สบายดีไหมคะ
How are you?
The two female endings have different tones: ค่ะ has a falling tone, while คะ has a high tone. Keep an eye on that little tone mark, too.
You can also add them to a thank-you: ขอบคุณครับ or ขอบคุณค่ะ. These endings add politeness; they are not a direct translation of “please”.