As you could see in that clip, impostors have an additional option – I clicked the sabotage icon on my overlay and chose to sabotage lights. That reduces crew vision, which means nobody saw me end poor Zeelubars’s life (I got away with that kill, and in fact me and Ben Weitz won that game easily).
Besides lights, you can sabotage different things on different maps, all of which makes the crew’s life harder. You can close doors, knock out lights or comms, or call reactor/oxygen and force them to answer the emergencies or die. The place to solve emergencies is always the same, specific rooms (like Electrical to fix lights), and anyone, crew or impostor can fix them.
This intro should be enough for you to get the basics of what’s going on, though if you watch a game or two on twitch you’ll be pretty much caught up. Let’s get to some strategy!