If you withdraw the principal from a roth IRA (as in, the amount that you previously contributed) do you have to fill out a special tax form?

Sorry for my ignorance, just was wondering. I'm able to do after-tax contributions to my 401k and have those convert to roth. But I could at some point in the future have a need to withdraw my contributions, prior to retirment.

In this situation, is there anything special I need to do from a tax perspective, to make sure that the IRS understands this is withdrawing of my previous contributions, not the interest/gains that they generated?