What would happen if you did something and did not tell?

Your question makes absolutely no sense. That or, it is extremely unexplained.

If you did something and did not tell? it depends..

crime- Get caught. go to jail

Something amazing- nothing at all

nothing of great importance- doesn't matter

lied- nothing if you dont get caught... OR

lied A; jail (under oath etc)

lied b: grounded (parents/gaurdians)

lied C: lose a friend

you get the point.