I don't know enough about Discord to know how useful an individual's Discord User ID is in actually finding/connecting with users. I usually just join channels/servers and see who's there. Am I doing it wrong?
That's more or less how I do it too; I find an invite to a channel I'm interested in, and people are there. You chat with who's there. But if you know someone's specific ID, you can PM them and chat privately. You can also see channels you have in common on their profile. PMs also persist across sessions, so you can always looks back on a conversation you had before too. Likewise for in channels, which is pretty useful, as compared to IRC, where you can't see anything that came before.