Dungeons & Dragons is a roleplaying game that uses an assortment of different dice, paper, pencils and rulebooks to simulate a fantasy environment where the players can create and roleplay heroic fantasy characters. At the most basic level, D&D uses three core rulebooks to play the game: the Players Guide, the Dungeon Masters Guide, and the Monster Manual. However, groups of D&D gamers may also use other books (there are a lot of these, produced by many different companies) and sometimes house rules. However, don't worry too much about it. Most gaming groups are more than happy to help a new player learn the rules. Any additional materials or house rules will be explained by your group as you learn. If it seems overwhelming, ask your group if you can stick to just what is in the core books at first.
Optional items that can be used for playing the game can include: miniatures to represent players, monsters and other characters, a 'battlemat' consisting usually of a soft, rubbery plastic material with 1" grids that can be drawn on with wet erase markers, and sometimes scale model scenery is also used. These items can be helpful in determining movement, tactics, and environment. Some groups use none of these things, other groups use them extensively.
Running the Game:
One person is the Game Master (GM, sometimes also called a Dungeon Master or DM) who is responsible for setting up the plot and running the other players through the adventure. The GM usually 'plays' the monsters and other Non Player Characters (NPCs) whom the players may meet in the course of the storyline. The GM may also use pre-generated adventures which can be bought from a variety of different stores/companies.
Playing the Game:
The players each use their dice along with a core rulebook (Player's Handbook) to generate their characters. Characters use 6 sided dice to determine ability scores (i.e. Strength, Intelligence, etc.) along with other necessary scores and stats such as Hit Points (the amount of damage the character can take), starting gold (to buy equipment, weapons and armor), etc. Players may choose between several races; elves, dwarves, humans, halflings, half-elves, etc. and also choose a 'class'; fighter, mage, ranger, etc. Characters can be simple or complex depending on how detailed your group decides to make them.
The actual game is run with a set of game rules which use dice to determine the outcome of combat, conflicts, skill results, etc. Imagination and description are key. Think of it as a story with the Game Master describing the setting, atmosphere and plot while you decide how your hero will react.
Starting Materials:
Necessary starting materials you will want to buy will include pencils, scratch paper, a set of dice (or borrow a set from a friend until you decide if you like the game or not). Core books can be bought, but most likely you will be able to borrow them when your group gets together to play since the other players will most likely own copies. If you decide to buy them, I'd suggest starting with the Player's Handbook. As a player you really don't need the other two 'core' books - Dungeon Masters Guide or the Monster Manual.
Dice used can be purchased in sets or as singles at many game stores, usually for around $6-8 per set and aroudn $.50-$1 per single die. You will want a full set consisting at a minimum of:
a four sided (d4)
six sided die (d6)
eight sided die (d8)
ten sided die (d10)
percentile die* (d00)
a twelve sided die (d12)
and a twenty sided die (d20).
(*a ten sided die used in conjunction with the d10 for determining percentages, numbered 10, 20, 30, etc.)
Alternately, you may want to pick up a few extra six sided dice since you generally use 3 or 4 to generate ability scores when you start making a character.
A NOTE on Miniatures:
Many D&D games use miniatures to represent player characters, NPCs and monsters. As a player, you will most likely not need to worry about buying a lot of miniatures unless you decide you really want to. You may be able to borrow a miniature to represent your character (if your group uses them) and eventually buy one if you like the game. Miniatures are like the books - they come in a huge variety, with several companies producing them. They come in plastic or metal, pre-painted or non-painted. Some of the non-painted minis require assembly. Some of the pre-painted lines come in randomly packaged 'boosters' but there usually is a secondary market for these as well if you simply want a single miniature. eBay is a good place to look for these. It is usually fairly easy to find one that looks like you imagine your character to look like. Once again though, check with your group before buying anything. Until you decide you like the game or not you don't want to sink a lot of money into it - especially if your group does not use them.
NOTE* There are many, many other books for Dungeons and Dragons. These usually fit into three categories; 'sourcebooks', world books, and adventures. Sourcebooks are books that expand on the selections for players. For example, the Book of Nine Swords (3.5 ed.) features three new classes (types) of fighter-type characters that players can play. Word Books describe settings and monsters for Game Masters to use for creating and running their adventures in. Adventures are pre-generated 'stories' that Game Masters can use. Generally, I'd borrow any books you need to get going before making any purchases. The sheer number of books can be overwhelming. Once you decide if you like the game you can look into purchasing other books that you might be interested in. A good rule of thumb when it comes to other non-core books though is to check with the person running your game to see if he/she will allow it to be used before buying it. Many sourcebooks introduce new classes, races, magic items, powers, etc. which your Game Master might not want used in his/her game.
As always, the object of this game - like any game - is to have fun. You are running a heroic character whose only limitations are the mechanics of the game, luck of a few dice rolls, and your imagination.
*NOTE* Dungeons & Dragons has seen several editions. The first edition was released in 1974 and was much simpler than the more recent additions. 4th edition is the current incarnation of the game and was released this year. 3rd edition was released in 2000 with an update to a '3.5' edition in 2003 which many groups still play. Most likely your friends are either playing 3.5 edition or 4th edition. Wikipedia has a more in-depth history of the game if you feel like checking that out.