Every country has its own tax system and so it is important to contact your local tax office to get up to date information. Usually you will have to pay some form of income tax on the money that you make from selling things commercially and if you send items to other countries you may have to pay an export tax. Unfortunately we cannot give you any specific advice about how much you would need to pay as it depends on a number of things (weight, type of product etc).
You can find a lot of resources about this online, however, if you have any doubts we always advise to check with your national tax office. They will be able to give you advice which is specific to your financial history.
If you are based in the following countries you can get in touch with your tax office using the links provided and selecting the contact option which is relevant to you.