If I withdraw money from my retirement fund, how will that effect my taxes when I file?

What type of retirement fund?   401(k),  Traditional IRA, Roth IRA, other?

It's just a 401K

A 401(k) distribution is taxed as ordinary income at whatever your marginal tax rate is depending on other income.     If you are under age 59 1/2 then there will be an additional 10% penalty for early distribution.  Many 401(k) plans do not allow distributions prior to retirement age.

If you take a Withdrawal it is taxable on your return and may push you into a higher tax bracket and more income can reduce or eliminate some credits you may qualify for.  So be careful.  Then there is a 10% Early Withdrawal Penalty if you are under 59 1/2 or under 55 if you left that job.  You can lose like up to 50% of it for taxes and penalties for federal and state.