Tabletop RPGs typically have a Games Master (GM) also known as a Dungeon Master (DM) and typically two or more players.
The GM is a sort of mix ot storyteller, referee and opposing player, controlling both friendly and hostile characters the players encounter, describing what they see and hear and telling them when they need to roll dice and what happens if they succeed or fail.
Typically each player plays one character they have created. Characters have a "character sheet" of stats and abilities so that the player knows what they can do and their probability of success at doing things.
To determine whether you fail or succeed at things, you generally roll dice (though systems that use cards or have no dice exist) which adds an element of exciting random chance and danger.
So let's imagine we're at a table playing Dungeons & Dragons (D&D), the most popular TTRPG. The Dungeon Master sits at the head of the table with a cardboard screen protecting their notes, and the players at sat around the table. Maybe there is a map on a wipeable mat, or maybe minis, but there may not be any visual aids at all.
DM is the DM.
Bob is playing Dax, a Human Fighter with a tendency to charge into combat.
Lucy is playing Aethen, a shy, book-smart but naive elf wizard.
Danny is playing Kogg, a grumpy dwarf cleric who he plays with a ridiculous Scottish accent.
Maya is playing Trixx, a hyperactive kleptomaniac halfling rogue.
DM: "You descend the timeworn steps into the dungeon, feeling the air grow increasingly cold as you go, until finally you stumble one by one into a musty room. It's dark down here, so Dax and Trixx, you can't really see much at all down here."
Dax: "I'm gonna light a torch!"
Kogg: "Ach, ya fool, human! There could be monsters!"
Kogg: "I wanna check if there are monsters with my dark vision."
DM: "Okay, roll a perception check."
Danny rolls a d20 and adds his perception score from his sheet, then tells the DM the total. The DM knows what number will be needed to see anything that is there, but keeps the number secret.
Kogg: "16!"
DM: "You see something stir in the corner of the room. It's about the size of a dog and furry, and it's watching you."
Kogg: "There's a wee beastie ahead!"
Trixx: "I want to try to hide! I roll a 12 for stealth!"
DM: "Um, okay, you can't see anything, but you can try..."
Aethen: "I want to get a pre-emptive hit on whatever it is! I CAST FIREBALL!"
EVERYONE: "AAAAAAAAA NOOOOOOOOO!!!"
Basically TTRPGs are great fun. They're imaginative, creative, sociable and research suggests they improve mental health, problem solving and empathy. It's a chaotic mix of improv acting with boardgames and a great way to spend an evening.
Over time, people get really attached to their RPG characters, and often pay artists to draw and paint them. It's hard not to become attached to an alter ego you regularly go on death defying adventures as.
If you want to know more, I recommend trying watching some of season 2 of Critical Role (the easiest season for a newbie to get into, I think) on Youtube, or try The Adventure Zone podcast.