Everything you need to know about broadcasting on steam is in your broadcasting settings page. Go to your top left corner of your steam window, then Steam > Settings > Broadcasting from the left menu
In this window, you just have to change the privacy setting to "Anyone can watch my games" in order to broadcast in public on steam
Yes, its recommended to have a good computer to broadcast something acceptable (i5 processor minimum/i7 processor recommended, a decent Nvidia or AMD graphics card) and a good connection as well. You should try to test broadcast to a friend that you know and trust so you could do some testing and see what settings you can broadcast well at. Usually, its acceptable and best to broadcast at 720p with a bitrate of around 2500-3000kb/s, but that of course depends on your system/internet capabilities.
If you have any more questions, just ask away