Where to start with Heretic?

Huge fan of classic Dooms. They are among the best games I have ever played. I played Heretic as a kid a little bit but I don’t remember it that much. So, I want to start playing Heretic again. I think I own them on Steam.

Which game do I start with? Should I play on Steam? Do I need to add any mods or anything?

Tank you ! (I’ve heard the enemies are tanky😛)