i'm quite a n00b on this whole Discord thing but the best way i can put it for fellow n00bs is that it's just a "private chatroom" where members are invited instead of just strangers hopping in at random (unless it's a public Discord)
It's a "gaming" app but nothing is stopping other communities from using it as well : >
Like i'm part of this specific webcomic's "Discord", it has a handful of members and a bunch of side "channels" to talk about other stuff than just said comic or general talk. You can of course just talk to specific members privately if you want to.
It's like your own little private forum? community? with your own little emotes and "roles" and sub-channels That you can access anywhere.
And just like any community, drama and misunderstandings can happen too.
Of course there is much more to it, but that's basically the gist of it.
Hope it helps x )