You have to add the computer as an asset that is to be depreciated in the Business Assets section (located under Business Income and Expenses).
Provided you have sufficient business income, you will be given the option to elect the Section 179 deduction toward the end of the process of adding the computer as an asset. You may also be given the option to elect the special depreciation allowance.
Further, if the computer cost $2500 or less, you may be able to expense it by making the de minimis safe harbor election.
