After you file

It depends, on your tax bracket. 

Generally, a conversion from a traditional IRA to Roth IRA is taxable unless you had an after-tax basis (nondeductible contributions) in your traditional IRA. You stated you had only made after-tax contributions and therefore only your earnings should be taxable at your regular income tax rate.

To confirm you reported the nondeductible contributions to the traditional IRA on Form 8606 in the previous years? If not, you can file the 2014 Form 8606 and 2013 Form 8606 without a return. Technically you can be fined $50 for failing to file the form on time, but the penalty can be waived if you have reasonable cause. Please see Relief for Reasonable Cause for additional information.

To enter the 1099-R conversion:

1. Click "Federal Taxes" on the top and select "Wages & Income"
2. Click "I'll choose what to work on"
3. Scroll down and click "Start" next to "IRA, 401(k), Pension Plan (1099-R)" 
4. Answer "Yes" to the question "Did You Have Any of These Types of Income?"
5. Click "I'll Type it Myself"
6. Choose "Form 1099-R, Withdrawal of Money from 401(k) Retirement Plans, Pensions, IRAs, etc."
7. Click "Continue" and enter the information from your 1099-R
8. Answer questions until you get to “What Did You Do With The Money” and choose “I moved it to another retirement account”
9. Then choose “I did a combination of rolling over, converting, or cashing out money.” and enter the amount next to "Amount converted to a Roth IRA account"
10. On the "Your 1099-R Entries" screen click "continue"
11. Answer "yes" to "Any nondeductible Contribution to your IRA?" if you had any nondeductible contributions in prior years.
12. Answer the questions about the basis from line 14 of your last Form 8606 and the value of all traditional, SEP, and SIMPLE IRAs