Ex: You give your sister a letter to give to your father and it's urgent. You find out after a week that your father still hasn't received the letter. So you call your sister and tell her 'you screwed up, I wanted that letter delivered on time'.

You use it when you tell someone to do something important on your behalf and he/she does not follow through with your instructions. Example: (1) I told you to pay the electric bill last week. Now we are going to get charged late fees. You screwed up. (2) I told you to bake the fish for 20 minutes. It's been in the oven for over 3 hours. You screwed it up. Hope that helps