Use Schedule C (Form 1040) to report income or loss from a business you operated or a profession you practiced as a sole proprietor. An activity qualifies as a business if your primary purpose for engaging in the activity is for income or profit and you are involved in the activity with continuity and regularity. For example, a sporadic activity or a hobby does not qualify as a business. This would be reported under other income.
Also, use Schedule C to report:
(a) Wages and expenses you had as a statutory employee,
(b) Income and deductions of qualified joint ventures, and
c) Certain income shown of Form 1099-MISC, Miscellaneous Income.
See the Instructions for Recipients (back of Copy B of Form 1099-MISC) for the types of income to report on Schedule C.
You may be subject to state and local taxes and other requirements such as business licenses and fees. Check with your state and local governments for more information.
Partnerships, joint ventures, etc generally must file Form 1065 or 1065-B.
For more information see IRS Instructions for Schedule C.