Capture card is not essential for the basic streaming, but in some occasions, it is necessary to use. The whole purpose of the capture card is, that your gaming device screen is by capture card transferred to another computer, which is serves as the streaming device.
AVerMedia Live Gamer Portable 2
There might be several reasons, when you shall use this set-up. The main reason is, that some gaming consoles do not allow you to stream directly on the internet or the features are limited compare to the computer streaming. The example can be PlayStation 4.
With the PS4 you can stream directly to many Platforms like Twitch or YouTube, but the problem is, that you loose all the features, which you can for example find in the OBS like a webcam, overlays, popups and many others. For this reason, the solution is to connect your console to the capture card, which transfers your picture and sound to the streaming computer.
You can even use the capture card while gaming on the computer. The reason for this is the efficiency of dual setup. Your gaming PC would not be slowed by the streaming, which commonly need high usage of your CPU power. This comes handy while playing games which have high CPU demands.
HOW TO SET UP CAPTURE CARD
If you decide you have a reason to buy a capture card and streaming from your gaming computer or directly from your console is not enough you might ask, how does it work.
The port on the capture card which is used for the receiving information must be connected to the HDMI on your gaming device. The outputs will be connected to the streaming computer and to your monitor (or TV). With this setup you are ready to go.
Next step is to chose on your streaming computer the streamed screen and sound from the capture card, this will ensure the transition to the streaming service of both sound and picture. Other peripherals like microphone, webcam shall remain connected to your streaming PC, since they will ensure the transition of these straight to your streaming PC, tough your stream. If you need a mic to be connected to your gaming rig as well (i.e. you are using in-game voice chat) you must use second microphone.
Nintendo Switch and the capture card
For connecting your Nintendo Switch to the capture card, you must put it to the dock and connect the HDMI cable from the dock to your capture card. After you will connect one HDMI to your TV from your capture card and second to your streaming computer.