Civilization V examines all of human history - from the deep past to the day after tomorrow. The "Game Concepts" portion of the Civilopedia explains some of the more important parts of the game - how to build and manage cities, how to fight wars, how to research technology, and so forth. The left Navigation Bar displays the major concepts; click on an entry to see the subsections within the concepts.
You can read all of the Game Concepts from start to finish, if you're the author's mom, but for everyone else we recommend that you start a game and check them out when you need them in play. If we've done our jobs right the in-game Tutorial will be all you need to do to understand how to navigate the early game.