Here are the steps, assuming this is for self-employment (not a W2 employee):
1) Go to Federal Taxes on the top menu bar
2) Go to Income & Expenses
3) Next to Self Employment Income, click Start.
The expenses interview will cover most common expenses; you may have to click the "less common expenses" link and enter some expenses within Other miscellaneous expenses.
The link below has additional tips for self-employment and side businesses:
Reporting Self Employment Income
Hope this helps.