I don't know everything about Discord... One function for Discord is live voice chat, so it is often used by multiplayer video gamers to run in the background and chat while they play. Another function is multi-channel, archived text chat with multimedia support for things like images and audio files.
Of note is that the voice channels use the "call" setting one your phone and not the "media" setting. Like Skype or WhatsApp.
I use it for two contexts.
The first is an online course I do. The course uses Twitch for its "live" video, but Twitch has a lag of about 15-30 seconds. Therefore, the course is simul-voiced through Discord voice chat (everyone but the professor is muted), and we use one of the text chat channels for questions and comments (this avoids lag and allows real-time interaction with the course). There is also another chat channel, unmonitored by the professor, for discussion among the students not intended for the immediate attention of the professor.
The second is for a local group to organize to play Pokemon Go in my (new) city. There are archived information-only channels where only mods can post. There are general chats for various topics. There are neighbourhood-specific raid organizing chats, and city-wide legendary raid alert channels.
The Pokemon Go one was my second Discord use, and I was surprised at how differently it was set up - it seems like it is highly customizable.
I mainly use it on my phone, but I also have used it on my laptop. But it has been a while since I used it on my laptop and I don't exactly remember how it is set up. I believe it is still under the auspices of the web browser, but it set up a shortcut on my home screen that went straight into Discord when launched.