If you're paid as an independent contractor on a 1099-MISC, then you'll enter those expenses by clicking on the Business tab (or Federal Taxes if you haven't entered your 1099-MISC yet), then the Income & Expenses tab, then scroll down to Self Employment and open the Income & Expenses section.
TurboTax will ask for your income entries first, then you'll see a button for Add expenses for this work. On the expenses screen you'll be shown a list of various expense categories to choose from, or you can scroll to the bottom and write in your own categories under Other Misc Expenses.
If you're paid on a W2 as an employee, then you'll enter those expenses by clicking on Federal Taxes, then Deductions & Credits, then scroll down to Employment Expenses (you may have to click on "See all tax breaks" to display the different headings). Then select Job Expenses for W-2 Income and follow the prompts.
