If you have expenses that are not reimbursed by your employer, or if your employer does not use an accountable plan, you'll generally have to claim the nonreimbursed expenses on Form 2106. In some cases you may be able to use Form 2106-EZ, Unreimbursed Employee Business Expenses.
Then the total amount of your expenses from either of these forms is transferred to Line 21 of Form 1040 Schedule A, Itemized Deductions.
The file is in Adobe Portable Document Format (.pdf), and you will need the free Acrobat Reader to view and print the file.