The use of "tell on"

[Tom]

Hi

I could not understand the use of "tell on" in my dictionary. Could you please give me a few examples?

Tom

[Conchita]

If I did something wrong and you told someone else, you'd be telling on me.

Another meaning of 'tell on':

If you don't get enough sleep, for example, and have dark circles under your eyes, then you could say that the lack of sleep is telling on you.