Chapter 1: Greetings & Politeness

ครับ and ค่ะ depend on you, not them
Thai politeness particles go on the end of almost any sentence. Which one you use depends on your own gender, not the person you're speaking to: men say ครับ (khráp), women say ค่ะ (khâ). They never change. Get these two right and you'll sound polite even when everything else falls apart.

Thai has five tones
The same syllable said at five different pitches is five different words. "Mai" can mean new, wood, burn, not, or turn a sentence into a question. This sounds alarming and isn't - you already do this in English when your voice rises at the end of a question. Thai just uses it on every single word.

Written Thai has no spaces
Words run together with no gaps: สวัสดีครับ is two words. Spaces appear only where English would use a full stop. It looks impossible now, and stops being a problem surprisingly fast - you learn to see word shapes rather than hunt for gaps.

Verbs never change
No I go, he goes, we went. Thai verbs have exactly one form, forever. Time is handed to a small word like แล้ว (already) or จะ (will), and everything else is understood from context. Whole shelves of grammar you had to learn for European languages simply don't exist here.

คุณ works for almost everyone
คุณ (khun) means roughly Mr, Ms and you all at once, and goes in front of a first name - คุณโรบิน, not คุณ plus a surname. Thai people use first names in nearly every situation, formal ones included.

The wai has ranks
Hands together, but how high matters: fingertips at the chest for friends and colleagues, at the nose for elders, at the brow for monks and royalty. As a visitor you are never expected to get this exactly right, and returning a wai politely is always better than not returning one.

There is a culture note for this chapter too - the thing a phrasebook will not tell you.