What do shutdowns and meltdowns actually look like?

I have read about shutdowns and meltdowns. But I don't actually get what that looks like in real time.

What I understand is that meltdowns is when someone loses control of their emotions.

Shutdowns are when someone loses the ability to perform certain functions, e.g. the ability to speak.

I was wondering if someone could give a more explicit example, of what that actually looks like?