What is the tax number at Twitch for?

To become a Twitch Affilate you have to give a tax number or something and what should you give it for and then do I have to pay taxes for it?

Where can I find the tax number?

If you earn something (certain amount per month) you have to pay taxes, of course, everything else would be tax evasion.

The tax number is on the top left of every income tax notice

Better not just put your parents' tax number somewhere