When you work as self-employed, you have to pay income taxes, just as an employee does. You would be exempt from income tax only if your income is lower than the income tax limit of 9000 € (as of January 2018). If you earn more as a self-employed individual, you should fill and submit a tax return to the local tax authority every year, before the 31st of May (deadlines differ from that of employees). You can learn about the process at http://www.elster.de/. However, the Elster portal could be difficult to understand and use, even for some native speakers. Alternatively, you can use online tools such as SmartSteuer.de for your tax returns. Keep in mind that filling your income tax returns could lead to financial gains, as you can deduct all your job-related expenses from your taxes. If you do not fill your income tax returns, the tax office will send you a reminder. In cases of continuous negligence, the Tax Office would independently estimate your incomes and costs which would most likely be to your disadvantage.
If you need help with your income tax return, you can contact a tax adviser or one of the payroll tax assistance associations, such as http://www.vlh.de/. Their service costs money, i.e. the fees you pay the consultant or the membership charges of the associations, but it can help you avoid unnecessary taxes and errors. If the Tax Office finds inaccuracies in your tax return, it can demand further payments later.
If you run your own business, you have to pay business taxes ("Gewerbesteuer") as well. The amount of your bussiness tax depends on where your company is located. If you earn less than 24,500 euros (as of January 2018) of business income per year, you are exempt from the business tax.
Besides, there is the value-added tax, which only applies if you have a turnover higher than 17.500 per year (as of January 2018)-such turnover means you are not categorised as a small business (“Kleinunternehmer”) anymore. Value-Added tax is normally paid monthly in advance. If you cannot afford it, you must apply for an exemption from the monthly prepayments at your Tax Office and justify your application. You can deduct the "input tax" ("Vorsteuer") you have paid to other companies from the Value-Added tax you pay to the tax office.