Yes if you are taking a withdrawal from a Roth IRA, then you will want to enter in the amount of all prior contributions. This will help the system determine if any of your Roth IRA distribution is considered taxable income and/or subject to an early withdrawal penalty. (If you are taking an early withdrawal of a traditional IRA, then you do not need to enter in any Roth IRA contribution information.)
You can always withdraw contributions (but not earnings) that you made to your Roth IRA tax and penalty free at any time. Additionally, the Ordering rules for withdrawals from a Roth IRA are: first from regular contributions, then from Conversion and rollover contributions, on a first-in, first-out basis and finally from Earnings on contributions. Therefore you will only have to pay taxes and possible penalties related to any earnings withdrawal. If your prior year contributions are not entered then the system may default to assuming the Roth distribution in the current year is from earnings and you will be subject to tax (and possible penalties) on the distribution.
Please refer to IRS - Roth IRAs - Publication 590 for more information about Roth IRAs.
To enter 1099-R information in TurboTax, log into your tax return (for TurboTax Online sign-in, click Here and click on "Take me to my return") type "1099r" in the search bar then select "jump to 1099r". TurboTax will guide you in entering this information.