Created in 1974, Dungeons & Dragons is a tabletop roleplaying game. What does that mean? A tabletop roleplaying game is a collaborative game where players work together to create a world and interact with that world's things. Players are led by a Dungeon Master (DM), the narrator of the game, and create characters through which they can interact with the world and each other. Using a set of seven dice, players roll to determine how actions can unfold.
Players use a set of statistics that can help determine the action's outcome along with their dice rolls. Characters have six core skills: strength, dexterity, constitution, intelligence, wisdom, and charisma. They also have select skills that they can be considered proficient in, meaning they get a bonus when they roll to use that skill.
Example scenario:
PLAYER: So I go up to the guard, and I'm going to try to get him to let me in.
DM: Ok, he looks at you as you walk up and asks, "Can I help you?"
PLAYER (in character): "The Captain sent me; he said that you would be able to show me the body. I'm an expert on… um, decapitations?"
DM: Make a deception roll.
PLAYER: I rolled a 15, and I have a +3 for proficiency, so that would be an 18.
DM: The guard narrows his eyes for a moment before shrugging and gesturing for you to follow him.
5th Edition D&D encourages a group of 3-5 players as an ideal party size. I have played in groups as small as 3 and as large as 8. I would argue that it is harder to play online with a bigger group, but everyone has their own preference.
What does 5th Edition mean? Since 1974, Dungeons & Dragons has gone through multiple updates and rule changes. 5th Edition is the current status of the game. The significant changes to D&D in 5th Edition are the renewed focus on roleplaying and character customization with a return to the game mechanics of previous editions, which had been dramatically changed in 4th Edition. Wizards of the Coast is the current publisher for 5th Edition D&D. The descriptions and alignment systems used on this site are all for 5th Edition; they may look different if you're playing a different edition.
There's other stuff, like casting spells, going into combat, and coming back from the dead, but let's not get ahead of ourselves. We're here to talk about the gods, so let's get to that.