Hi! I want to start streaming on Twitch, but I've read that you also need streaming software, what for?
You have to somehow get your picture of what you want to stream on Twitch. The streaming software does this, captures your picture and sends it to the Twitch server so that the others can view it.
Ah OK thanks. I heard OBS is good, right?
Using the software, you select which content you want to stream (e.g. Only 1 of 2 screens), set overlays (chat semi-transparent on the right side + possibly donation goals or similar).
The software then compresses the content, authenticates itself with your username or a key and sends the finished content in a suitable format to the service's servers, e.g. Twitch or YouTube.
Undifferentiated question: so undifferentiated "yes, it is good". XSplit Broadcaster would be an alternative.
How else did you imagine how what you want to stream would end up on twitch?
With the streaming software you transfer what you want to transfer and you can make further settings, e.g. Fade in chat, a facecam from you so that you can be seen, if necessary, if someone subscribes to the person is displayed, etc.
Twitch can't smell that you want to stream and does it automatically.