Earn money on the Internet - register individual trades / taxes?

Okay, you can make money on the Internet in a lot of ways.

Surveys, only fans, Patreon, Fiverr, NSFW adult content (on corresponding websites, or on their own website), with Instagram, with Youtube, with Twitch, their own blog, on Etsy / Ebay / Amazon / etc. Selling homemade things, e-sports, and so on.

But in the end you have to register a single trade (or something like that), right?
And what about taxes?
Everything has to be legal, otherwise it's illegal work and then you end up in jail.
Or do you only have to start from a certain income?

But how does one do it? Where do you go?

To the trade office

But I can hardly say to them, "Hey, I want to make money with pictures of my feet"._. Or, other, more embarrassing things.

You should make a business registration.

A single company is sufficient for this.

Here is an overview of the possible company forms:
https://www.junge-gruender.de/unternehmensformen/

If your sales are small you could use small business regulation:
https://www.lexoffice.de/gesetzesaenderungen/kleinunternehmerregelung-2020/

With one registration all institutions (tax office…) are informed. Maybe you should start doing it part-time.

You have to keep an appropriate bookkeeping. It should be clarified what is with your health insurance company. How it is with the trade association.

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Now another advice for doing business on the Internet.

Note the possible costs of returns
Bet on several areas
People who only see ads from e.g. Put Adsense or YouTubers ultimately have only one customer Google and wants coal coal coal. As soon as the programs bring less money - which I currently read very often - you have nothing.

Similarly careful with sales at Amazon, always several irons in the fire.
Take into account GDPR websites and mandatory information, otherwise there may be expensive warnings.
Reach in social media quickly becomes chargeable.

Then you just write "model" or "services for natural and legal persons".