From a financial accounting standpoint, your profit or (loss) is simply your total revenues - total expenses. So let's say you ran your business for 1 year and were paid a total of $40,000 by your clients during the course of the year. Let's then assume that you had total business expenses of $10,000, including supplies, insurance, depreciation, interest, etc. Your "profit" would be $40,000 - $10,000 = $30,000.
From a tax perspective, it is a bit different because some of the expenses that you claim for "financial statement purposes" are treated differently for tax purposes. For example, on the above hypothetical, let's assume your equipment costs are $15,000 (camera body, lenses, lighting equipment, etc.). For financial accounting purposes, you may depreciate the equipment over a period of 5 years, so you would claim a deduction of $3,000 per year for financial accounting reasons ($15,000 / 5 = $3,000 per year). For tax purposes, however, you may depreciate the same equipment over a different period of time. Assuming a 3 year useful life for tax purposes, you would claim a tax deduction of $15,000 / 3 = $5,000. So your tax depreciation is different from your accounting depreciation.
Make sense?