Some of it depends on what service you are using to stream. Livestream.com for example supplies their own software to use with a video capture card. Others will work using the free Adobe Flash Media Live Encoder.
In both of those cases you will need to get a video capture card because the built-in USB 3 port requires using a very specific chipset on your computer which is hard to get ahold of these days.
If you have a thunderbolt equipped computer you can get an UltraStudio Mini Recorder for ~$145, or if you want to go completely computer-free you could get a box like the Teradek VidiU or the Matrox Monarch HD.