A country that would give a little freedom for a little security, will deserve neither and lose both.
*Ben Franklin
The Basics
You need a group of people... a DM (Dungeon Master for you newbs), and at least 3 gamers with a few hours to kill. I will walk you through how to start up and play D&D 2nd Edition.
First you have to get a some dice... six 6-sideds, two double-sided 1-10's (percentiles), two 8-sided, two 12-sided, two 20 sided, and one 4 sided. These are the minimum ammount of dice for a standard begining game.
DM needs to have all his shit together and have maps, quests, alternative things in case the party of gamers decides not to take the intended route of action. If you want it to be a good dungeon and last a few years, you should just make it all yourself. It will take you a long time to do this, but makes the gaming experience a lot more interesting if you get creative.
As DM you should have a good deal of books for you and your group of friends. DM should have a couple of monster manuels, dungeon master's guide, gods goddesses and dieties book (for clerics and other religious characters), and a couple hand books for players. These could include spells, creatures, and brief over view of the rules of the game.
