RPGs (Role Playing Games)
have been around in their current form for about 40 years, since the release of the first Dungeons and Dragons book back in 1974. D&D grew out of wargaming with miniatures and was created by Dave Arneson and Gary Gygax, pictured here from the cartoon Futurama.
To play a RPG, you need a basic set of rules. It's never been safe long-term to develop material using official D&D branding elements and material even as they offered various types of licenses over the years. So Stuart Marshall and Matthew Finch made the rulebook OSRIC
which basically recreated D&D 1e within the OGL (Open Gaming License)
. This means that anyone can publish material that uses OSRIC without worrying about what WotC or any corporation thinks about it. You can get OSRIC for free.
On its most basic level, tabletop RPGs are collective storytelling among a group of friends. There is a Dungeon (Game)
Master that monitors and controls the action and dispenses the story and the players who are engaged as characters within the fantasy world. Dice are used as randomizers throughout to decide the how various things will work out. You have a character sheet that tells you your stats, inventory and other data, and a paper map that is being revealed as you move through the world/adventure. Besides a map, maybe a handout and some illustrations, the entire game takes place in the imaginations of the players.
One place to start is with this free Introduction to Playing Original D&D
by Matthew Finch.