Do I have to pay attention to something?

I'm 14 years old and I plan to start streaming Minecraft on Twitch soon.

I don't want to make any money, I do it for fun.

Do I have to pay attention to anything?

First of all, your parents should allow it and also know exactly what you are doing.
Everything else, at least as far as the legal stuff is concerned, should be itemized in the terms and conditions.

Make yourself aware that you are then on the Internet and that everyone can access it. It can always happen that someone who shouldn't see it (from school) hears about it and starts annoying you with it.

And before you start you need your parents' permission.

Otherwise, I would say you need a decent microphone and do not use the headset that comes with a newly purchased cell phone, but buy some better equipment. Of course you don't want to earn any money, but quality is still important otherwise you only stream for yourself.

If you go through the roof with a concept that stands out you should see how you start to make it a little more professional so as not to appear low quality.

However, don't be too disappointed if it doesn't get you famous.

I don't want to make any money, I do it for fun.

Do I have to pay attention to anything?

No donation button & certainly not offer an affiliate.
You are not allowed to do the latter anyway.