What is Slack? And what is it used for?

When I first used Slack back in 2015, I could not for the life of me wrap my head around the concept of threads. Now, after a decade or so of Slacking, I’m the person passive aggressively reminding people to please respond in threads for the love of all that is productive. That’s all to say: I know what it’s like to completely not understand Slack—but I also know enough to help you understand it.