Going to school, and am still confused about withdrawals from retirement account

[hashbrowns]

Hi, I'm a mechanic working towards a Mechanical Engineering degree. I've been contributing to a 401k, Roth IRA and a taxable account. When I complete this associates transfer degree I plan on attending university full time and hope to scrape by with odd mechanic jobs, on campus work, grants/scholarships/loans, and the support of my fiance.

I've read through the IRS website, and this site, along with wasting extensive amounts of on-the-clock time googling whether I can make withdrawals from my previously mentioned accounts, to pay for school related expenses, without being ripped a new one in taxes. I'm newer to paying attention to my financial wellness, so please forgive my ignorance, but I am still confused about making withdrawals.

From what I've seen I'm allowed to withdraw what I have contributed to these accounts, but I cant take out dividends? Is it as simple as that? If I have trouble making ends meet, having this money to fall back on would be a huge comfort.

This all is the reason I have the taxable account too. I was previously under the assumption that I couldn't touch my retirement accounts so I was going to build up my taxable account so I could access it.

[MDM]

I've been contributing to a 401k, Roth IRA and a taxable account. When I complete this associates transfer degree I plan on attending university full time....
...
whether I can make withdrawals from my previously mentioned accounts, to pay for school related expenses, without being ripped a new one in taxes?
...
From what I've seen I'm allowed to withdraw what I have contributed to these accounts, but I cant take out dividends? Is it as simple as that? If I have trouble making ends meet, having this money to fall back on would be a huge comfort.

Two things:
1) Normal taxes
2) 10% extra tax (aka "penalty") for some IRA withdrawals prior to age 59.5.

Taxable account: Tax due on withdrawal if a contribution has increased in value (aka, "had a capital gain").  Amount of tax depends on whether it is a short or long term capital gain, and your total income.  No "extra tax".

Roth IRA: No tax due on withdrawals up to the amount you contributed.
Traditional IRA: Normal tax due on any withdrawals.  Amount of tax depends on your total income.
Either IRA: No "extra tax" if withdrawals used for qualified higher education expenses.  See Retirement Topics - Exceptions to Tax on Early Distributions.  Other exceptions are possible, but absent education or another exception, there is 10% extra tax also due on any taxable withdrawals.

401k: Normal tax due on any withdrawals.  Amount of tax depends on your total income.  10% extra tax also due on any withdrawals.  If, however, you have left the company where you contributed to the 401k, you can roll the 401k over to a traditional IRA - then see above for IRA treatment.