Okay . . . <*cracks knuckles*> . . . where to begin?
First, obtain the the core rulebooks. At 1st edition, they were the Dungeon Masters Guide (DMG), the Players Handbook (PHB), and the Monster Manual (MOM). A DM's screen is very helpful, too. You can also obtain (or download for free) some pre-made adventures -- I strongly recommend this.
Note paper, graph paper, polyhedral dice, pencils, and markers or minatures (Minnies) are also necessary.
Oh, and a place to play, too!
Currently, the game is in its fifth edition (5e). There is a Starter Set available.
Second, STUDY the material. Don't just give a single read-through and think you have it covered. You need to KNOW the material.
Third, roll up a few characters of your own. Not only will this help familiarize yourself with the system, but you will have some spare characters to use as non-player characters (NPCs), spare player characters (PCs), or one of them could become your primary favorite character to play.
Fourth, gather some like-minded friends. I have seen groups of 2 to 7, plus the dungeon master (DM). I am most comfortable with only 4 or 5 players, although having only 2 or 3 players can be fun, too.
Finally, keep notes -- who did what where and when. Basic stuff -- a log, not a novel.
Oh, and remember the Golden Rule of Gaming: "The most fun, for the most people, most often".
Link to the Official D&D Website
_________________
No love for Hamas, Hezbollah, Iranian Leadership, Islamic Jihad, other Islamic terrorist groups, OR their supporters and sympathizers.