You’ve got the DM bug and want to run your own games. If you’ve never DM’d before, you’ll want to pick up the D&D Starter Set – it will explain how to play D&D as the Dungeon Master and includes an adventure to run with your friends. You can DM this adventure (The Lost Mine of Phandelver) at home, online, at a store, or at a convention. Either get your own group together to play privately or contact a local store or convention organizer to run a game at their location. The Basic Rules are online for free in two different free versions, a downloadable PDF (both for Players and DMs) and an online interactive document.
If you’re an old hat at DMing the above applies to you as well, but you might also want to run other games. If you can run only weekly 2 hour games on Wednesday nights, DM D&D Encounters. If your schedule is more sporadic or you want to run full adventures in about 4 hours, go with D&D Expeditions. You can contact your local convention or game store for more information about becoming a store organizer. If you enjoy running dramatic games at conventions, find out about conventions running D&D Epics and ask to join their cadre of DMs.