How do I do it? I want to stream Crash%.

You need to buy and install a capture card.

oh ok thanks but where does the capture card go?

It needs to be installed into the hardware of the console. That can be done by you through soldering (I think, at least, I'm not familiar with 3DS capture cards) or by usually the seller who offers an installation service too if you send them your console.

of course right as you had done that i figured it out (i think)