There is no federal deduction for making a contribution to a 529 plan. So, there is no place to enter it, in the federal interview. Some states allow a deduction on the state return. If your state is one, it will come up in the state interview; usually in the "Here's how (your state) handles income differently" section.
For a state list of eligible plans, see: https://www.savingforcollege.com/529-plan-details
http://www.savingforcollege.com/compare_529_plans/index.php?page=compare_plan_questions&plan_questio...
The tax break comes in the future, when you take the money out to pay for education. All earnings (interest, dividends and capital gains) over the years is tax free if the distribution is used to pay for education, including room & board.
