The most common itemized deductions, which you don't claim if you use the standard deduction, are medical expenses, state and local income tax, sales tax, or property tax, and charitable contributions. If you know you are going to use the standard deduction, you don't have to enter any of these.
NOTE: See Opus 17 answer for how TurboTax actually handles the entry of itemized deductions in the Free Edition. The above description is not accurate.
Turbotax is designed to ask you about all deductions and then decide for you if it should itemize or use the standard deduction. (This also has the effect of getting people to agree to upgrades that they might not need.) You should be able to skip the itemized deductions. Look for "skip" or "finished" at the bottom of the page listing itemized deductions. You may have to scroll down if it doesn't show right away. Once you indicate you are "finished" with your deductions (even after not entering any), it may nag you a bit ("are you sure you don't own a home/have education expenses/etc") but it should allow you to finish the federal taxes without itemizing.