Unlike contributions to a traditional IRA, you get no tax deduction for contributing to a Roth IRA because you must contribute after-tax money to a Roth. The tax break comes later: Follow the rules, and all the money in your Roth IRA can eventually be withdrawn tax-free.

SEE ALSO: Why You Need a Roth IRA

You can withdraw your contributions immediately, at any time, because the contributions are after-tax money. But any earnings on a Roth IRA can't be withdrawn right away. For earnings to be tax-free, you must meet two tests: First, you must be 59 1/2 or older; and second, you must have had at least one Roth IRA open for at least five years.

If you convert money from a traditional IRA to a Roth IRA, that money has a restriction on free withdrawals, too: For converted amounts, account holders younger than 59 1/2 must wait five years before they can tap that converted amount free of a 10% early-withdrawal penalty. The good news is that money withdrawn from a Roth is considered to be contributions first, then converted amounts, then earnings, according to IRS withdrawal rules.

SEE ALSO: Consider a Roth IRA for Tax-Free Income

Any taxpayer can do it -- even teenagers with earned income. What's more, there's no maximum age limit for contributing to a Roth IRA. As long as you have earned income (or a spouse who earns income), you can put money into a Roth.

The annual IRA contribution limit, which for 2015 is $5,500 (plus an extra $1,000 for those 50 and older), applies to your IRAs in total. So for 2015, for example, a 30-year-old could split her total IRA contribution and put $3,000 into a Roth IRA and $2,500 into a traditional IRA. But keep in mind that the contribution limit is capped by your earned income: If you made only $5,000 for the year, you can only put in up to $5,000 into your IRA and Roth IRA combined.

There is an income threshold for making Roth contributions. The cutoff for contributing to a Roth IRA for 2015 is an adjusted gross income of $193,000 if married filing jointly, or $131,000 if single. The size of your contribution will start to phase out if you earn more than $183,000 if married filing jointly or $116,000 if single. But these high incomers can still get money into a Roth by putting money into a Roth 401(k), if their company offers it, or by converting money from a traditional IRA to a Roth IRA. Anyone can do a Roth IRA conversion; there are no income limits for making that move.

SEE ALSO: How Much You Can Contribute to Retirement Plans in 2015

Unlike traditional IRA owners who must start taking required minimum distributions at age 70 1/2, Roth IRA owners never have to take RMDs. A Roth IRA owner can choose to let the money sit in the account and grow tax-free for as long as he lives. If a person makes an annual contribution of $5,000 to a Roth IRA every year for 40 years and the money grows at a 6% annual rate, he'll end up with about $1.07 million -- all of which can be withdrawn completely tax-free.

Some companies offer a Roth 401(k), although that option isn't as common as the traditional 401(k). If your company does offer a Roth 401(k), you can choose to put all of your contributions into the Roth 401(k) or you can split your total contribution between the traditional 401(k) and the Roth 401(k). (The 401(k) contribution limit for 2015 is $18,000 for young workers and $24,000 for workers 50 and older.) Note, though, that any employer match you receive will be put into the traditional 401(k).

SEE ALSO: Invest in a Roth 401(k) If You Can

After the original owner of the Roth IRA dies, a nonspouse heir (perhaps an adult child) who inherits the Roth IRA must take required minimum distributions if he wants to keep the money in the tax shelter, though he won't have to pay income tax on the distributions. The nonspouse heir can stretch the distributions over his own life expectancy, though distributions must start in the year following the original owner's death. But a spouse who inherits a Roth IRA gets a choice: She could remain a beneficiary, which would require her to take RMDs, or she can take the Roth IRA as her own account -- and that would allow her to avoid RMDs.

SEE ALSO: When a Spouse Inherits an IRA

Be careful. When you convert money from a traditional IRA to a Roth IRA, the amount you convert gets added to your taxable income for the year. So if you convert $10,000 and your other taxable income is $50,000, your total taxable income for the year will be $60,000. If you convert a large amount of money, you could easily push yourself into the next tax bracket -- or even into the top tax bracket.

By pushing your taxable income up, you could also trigger other tax events, such as getting hit with Medicare premium surcharges or phasing out of certain income tax deductions. Carefully estimate the impact of a conversion on your overall tax liability before you make the move. A smart strategy is to convert only an amount that will keep you within your expected tax bracket for the year.

A Roth IRA conversion offers a mulligan. You can "recharacterize," or reverse, a Roth IRA conversion up until October 15 of the year following the year you did the conversion. If your account value dropped, for instance, you might want to undo the conversion so you won't end up paying a tax bill on money that's no longer in your account. You can always choose to reconvert the money -- you just have to wait 30 days or until the following year, whichever comes later. Note: You can also convert traditional 401(k) money to a Roth 401(k), but that conversion cannot be recharacterized.