Well lets start off with what a Table-top RPG is. Its a form of interactive story telling with two job types.
1.The DM- The person that sets the stage, sells the world to the players, and comes up with the story (or bases it off of an adventure module). They run the game, enforce the rules, and try to get the players to assume their roles, act, and play along (No you can't has a box of grenades in Call of Cthulhu. WHY WOULD YOU CASUALLY HAVE THAT?....now if its a more comical game that could slide.)
2.The Players- The People that make the game work. Without the players the adventure would just be a very boringly written story. Its their job to play roles and make the story work. If a player is playing a street wise theif who needs to learn some information from the street, why would one just go "I use street talk to gather information?"
Monster books are bestiaries that give you pre created monsters to use in the game. This is good because creating monsters especially varied monsters that get the characters thinking tactically, are daunting to create. So its best for the DM to research monsters and pick out the ones that fit the adventure rather than creating monsters themselves.
These games require prep time because a DM needs to craft the adventure. This isn't a video game that is finished when you get it, this is an analog interactive game that can grow and change as time progresses.
But since I'm writing a comic series I don't see this as a huge problem. Oh and non pro tip. STAY AWAY FROM THE D20 Call of Cthulhu. D20 is combat based. Call of Cthulhu isn't.
[link]For further information I recomend you watch some of these. I'd reccomend you watch the Thieves' World videos, Tandem's Last Ride, Getting Started with Role Playing, DMing a great game, and then Never get on the boat to the most recent video. You don't have to watch these but they help in understanding what a table top RPG is.
Plus they're funny.