Well. There are a few places around. The big ones are places like libera.chat, oftc.net, etc. Those are HUGE though (By irc standards) so sometimes it can get overwhelming trying to find somewhere to just hang out and chat. Slightly smaller servers tend to work better as an introduction, at least to me. Things like tilde.chat which has a clearly defined main chat area, and a lot of more niche chats for things you might be interested in.

Generally, if you get started on one server, and make some friends, join a few channels, find some interests, you'll find your servers expanding. It's a large enough ecosystem to have a LOT of people, but small enough that you'll bump in to people you already know if you try multiple servers. Which is nice.