To 'kid' can mean to joke about something.

"The zookeeper was kidding when she said the snake will bite me."

It can also mean to not tell the truth.

"I've been kidding him for a few years now and he hasn't realised that I'm not telling him the truth."

These expressions that involve the word 'kid' are commonly used in everyday speech:

Just kidding

We use 'just kidding' when we're talking about something and we don't want people to talk it seriously.

A: "There are two things I'm really, really afraid of. One is a snake and the other is my mum."

B: "Oh really?"

A: "Well, I'm just kidding about my mum."

No kidding

We use 'no kidding' to emphasise what we're saying.

"I spent the whole day cleaning my house, no kidding!"

You must be kidding/You have to be kidding

We use 'you must be kidding' to react to what a person is saying. You usually say 'you must be kidding' because you don't believe what the person is saying.

A: "I took two hours to make this cake."

B: "You must be kidding. Did it really take that long?"

You can also say: "you must be joking".

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