Here's a quick cheat sheet for those that don't know, or haven't played with this ecosystem.
BitFocus Companion is community developed and free piece of software that is the glue to connect a lot of different things from various surfaces. It is essentially a "hub" where inputs and outputs from audio and video systems can be absorbed, and triggered based on scripts or user input. In short, its a configurable server that runs on MAC, PC, or Linus (even a Raspberry PI).
User inputs? How? The most common way is through a very common and reasonably priced piece of hardware called Stream Deck made by a company called Elgato. Stream Decks are USB devices that plug into your computer that have "soft buttons" that you can assign tasks to. Without connecting to Companion, you can create and assign buttons to do things to help with your video editing, or gaming, or streaming.
Basically its a big LCD screen under some clear soft buttons. By using StreamDeck software you can create buttons for everyday tasks. If paired with the BitFocus Companion software, then these buttons can start doing quite a bit more stuff in your streaming or production environment.