When I first decided to get into Brood War from Starcraft 2 I noticed it was hard at first to find out where the community was hanging out.
I found the Brood War beginner guide on liquepidia liquipedia.net and a few discord servers there were listed.
To make things easier for new players I'm going to post some Discord channels which I have found from multiple sources.
Please add more Discord channels if I have missed any!
Coach Pupil League (CPL)
discord.gg
An excellent learning community and providers of the CPL league for new players. So far I have found this one of the most active.
ShieldBattery
discord.com
ShieldBattery is a custom server and launcher client for StarCraft: Remastered, adding many features and improvements while utilizing the real game client for gameplay. It is a community-run project under active development, with new features added all the time! More and more people are joining it as B.Net Ladder is at times inconsistent and contains bots.
Brood War Clan League (BWCL)
discord.com
The Brood War Clan League (BWCL) is the oldest and still active foreign clan league. Joining the BWCL Discord is also a good idea if you have any interest or general questions about the league, even if you are a solo player looking to join an already participating clan.
Bombastic StarLeague (BSL)
discord.com
The "Bombastic StarLeague" is a tournament series organized by ZZZero and BSL staff to support StarCraft and StarCraft:Remastered community outside of Korea. BSL started as a tournament only for Polish players, eventually becoming the biggest online tournament in the scene.
Foreign Brood War
discord.com
Foreign (non-Korean) Brood War community on Discord. Sometimes active.
Brood War UMS
discord.com
A community for fans of Brood War UMS (Use Map Settings) custom games. UMS maps provide custom game modes different to the original game. I haven't entered this Discord yet.
No Hunters Free For All
discord.com
A casual community with an interest in playing Melee, FFA and different types of team games.
/r/starcraft
discord.com
The Starcraft subreddit Discord server. Broodwar section only sometime active.
Inside these discord channels you may find links to even more channels. Such as the following. Note that some of the below links may contain paid content.
Terran Academy
discord.com
Terran Training
The Rise of Aiur
discord.com
Protoss Training
School for Zergs
discord.com
Zerg Training
Spawning School - Translations & Guides
discord.com
Translated zerg training videos.
I hope this helps!