Rollover IRA penalty

Hello, I am looking into withdrawing from my rollover IRA to help pay some bills/credit card debt and I was wondering how the penalty and taxes work? This IRA was originally a 401k with my original company but was changed into a Rollover IRA once my company was acquired. Since I am under 59.5 I know there’s a penalty and I’ll have to pay taxes on it but I’m confused on when I’d pay this penalty. Is it up front or when I file my taxes? Thanks for the help