Are you an employee? If you are an employee then any of your real estate agent expenses will go on schedule A as employee business expenses.
Click on Deductions and Credits, and scroll down until you find Employment Expenses-W-2 Income
If you are self-employed, than both your commission income and your expenses will be reported on schedule C.
Click on the search box and type "schedule c" and press enter. A Jump To option will be available.