If you have a 100% outside scholarship it will cover 100%. You’d get nothing from the school but you’d nothing.
If COA is $60k, and you have and EFC of $20 and the school awarded you $20k, you’d still need $20k which might be made up of work study, loans, perhaps even a ‘gap’. Say you get $30k in outside awards. It is likely the school would use that for the $20k in work study, loans, etc, and might reduce the school aid to $20k You’d still owe your EFC of $20k.
If your outside scholarships are only for $5k, they might apply it all to the third category of loans and workstudy and let you keep all the school aid.