A layman deskription would be that a traditional IRA gives you a current tax deduction, meaning you will be able to reduce your taxable income right now. Say if you are currently on a 25% tax rate, by contributing 5500 (Maximum for age 50 or under), you save $1,375 right now. You pay tax when you distribute the principal and the growth. Also, If the contributions are with drawn before you are 59 and 1/2 year old, you pay early distribution penalty of 10%.

Roth is a post tax contribution, which means you pay tax right now but you do not pay tax on the distribution of principal and growth.

So the bottom line is if you want to save tax right now or in the future. Also, most of us don't think about retirement right now but its never too early to put aside some money for our future. Can't count on the kids to take care of us these days :)