Well Melza, allow me to provide an alternate perspective.
Roleplaying in wow in its most basic form is about taking the story of Warcraft as it is being told, and imagining your character as one of the adventurers/heroes out in the world. A Dwarf with a dwarf-sounding name and an awesome transmog set can be roleplaying as a fierce warrior of the Dwarven Clans and a Champion of the Alliance… even if all they did was actual content, PvP, PvE, dungeons, battlegrounds, raids, quests. The story of that dwarf is inside their player’s head, but it does not make it any less of a good story.
Immersion is a thing on the roleplaying servers. The most basic rule of RP realms is that your character name needs to be fantasy-sounding, not a reference to Real Life, other fantasy genres or composed of 3 or more words. “Bonechewer” is still a perfectly sounding fantasy name.
Heavy Roleplayers (most that recruit to dedicated RP guilds) take it a step further and think of a story to their character, where they are from, what do they aspire for, what kind of person they are and toss themselves to interact with other players, creating an illusion of actual living and breathing denizens of Azeroth. They usually picture their character as something a bit less heroic and flock in guilds that might, for example, try to roleplay Trolls as accurately as possible as given in lore and go on wild adventures to hunt some heads to shrink.
What makes it enjoyable? Well, the same reasons you might enjoy reading a good book, except that your character is also a person in the story and has a direct impact where the story goes. Roleplayers are all storytellers in some shape or form.
You are also correct that roleplaying servers (in general) are much more relaxed and mature environments to play. That is also why I personally came to RP servers years ago.
Being a casual player and not really knowing about roleplaying is fine. As long as you do not intentionally disrupt those who do roleplay and try not to break their immersion, you two can coexist just fine.
When you feel comfortable, you can always go and attend to some of the public RP events. Plenty are advertised over forums, and on the Argentarchives website (which is an external, AD focused roleplay supporting site).