别【bié】

别 before a verb tells someone not to do something. 你 can go in front or be left out.

别…了 for "stop"

With 了 at the end, 别 tells someone to stop what they are already doing, or to drop a plan.

Without 了 it is a general warning, often before the thing starts.

Only for telling people

别 is for commands and advice. A statement about what someone isn't doing takes 不.

• × 我别去 → 我不去
• × 他别喜欢咖啡 → 他不喜欢咖啡

不要 also means "don't" and works the same way in commands; 别 is shorter and more common in speech.

别太 and set phrases

别 + 太 + adjective warns against too much of something. 别客气 answers thanks.