People who want to get into Dungeons & Dragons and need an introductory adventure can get some great ones for free, courtesy of Wizards of the Coast. There are lots of D&D Starter Sets to choose from, which are physical boxsets that contain dice, pre-generated characters, simplified rulebooks, and short campaigns that are designed to be easy for DMs to run. The DMs who don't mind running their game from their laptop or phone can do so without paying any additional cash, as the official D&D website and D&D Beyond have adventures and campaigns that can be played for free.
There are many DMs who prefer to create their own homebrew adventures, while others like to buy the pre-made campaigns released by Wizards of the Coast. Either of these options can require a lot of prep time, which isn't always feasible, even though many modern D&D campaigns tend to be episodic in order to make them easy to run without knowing the ins and outs of the story. It's for this reason that D&D adventure anthologies have become popular, such as the recent Journeys Through the Radiant Citadel adventure anthology, where DMs can pick and choose from the selected adventures and run them in isolation.
All that is necessary for playing D&D are the three core rulebooks: Player's Handbook, Dungeon Master's Guide, and Monster Manual. The D&D Starter Sets sidestep this, by including everything within the boundaries of the adventure (including magic items, spells, and monster stats) in its rulebooks. The three core rulebooks provide everything for amazing D&D homebrew campaigns, but they don't have any pre-made adventures for new groups to run. There are lots of great adventures available online that are free to download, some of which are provided by Wizards of the Coast itself.
D&D's Death House Is A Great One-Shot Halloween Adventure
Death House is an introductory adventure that can be downloaded on the official Dungeons & Dragons website. The intention is for Death House to act as the lead-in to the famous Halloween-appropriate Curse of Strahd campaign, giving players a first adventure when they reach Barovia at the beginning of the campaign. The players are led to the Death House by the ghosts of children who perished there in the past, and they encounter the evil creatures that hide in its dark corners and secret passages.
It's easy to play Death House in isolation and to keep its backstory to a minimum, with the goal of the adventure being to simply solve the mystery of its haunting and to defeat the creature in its basement, without needing to tie it too firmly to the Ravenloft campaign setting. Death House works great as a D&D horror-themed Halloween one-shot adventure. DMs should bear in mind that Death House has some dark content, such as the death of children, which some players might not be comfortable with.
D&D's The Lost Mines Of Phandelver Is Designed For New Players
Many D&D groups had their first experience with 5e through The Lost Mines of Phandelver, which is the mini-campaign that comes with the first D&D Starter Set. Those who want to play The Lost Mines of Phandelver can now do so for free, as it's available to everyone who makes a D&D Beyond account. The Lost Mines of Phandelver has two segments at the start of the adventure that can be tailored for an exploration/combat-heavy one-shot, but the entire campaign has lots of content for multiple sessions worth of play. Ultimately, The Lost Mines of Phandelver is about dungeons and combat encounters, but there is some opportunity for roleplay as well. Players will also be able to return to the town when the D&D Phandelver campaign launches in 2023, turning the classic starting town into the basis for a cosmic horror adventure.
D&D's Hoard Of The Dragon Queen Throws Players Into The Action
When a D&D group mostly consists of new players who are strangers to one another, the best way to introduce them into the game is by throwing them into the action. This prevents boring or slower moments from occurring during the early hours of the game, as people are more likely to be more cautious around those they don't know and less willing to get into character. The introductory adventure for Hoard of the Dragon Queen on the official Dungeons & Dragons website is a great way to give D&D's newest players the most focus and keep them moving in a structured way. Hoard of the Dragon Queen has Adventurer's League content at the beginning, but this is easily skipped and isn't vital for the adventure itself.
Hoard of the Dragon Queen kicks off with the players acting as caravan guards on a journey to the town of Greenrest. When they arrive, the town is attacked by the Cult of the Dragon, led by a blue dragon. The opening act of the adventure involves a running battle through the town, with some easy encounters that can be used to teach players about the combat rules. Once all of the surviving citizens make their way to the nearby keep in the town, the players then go on missions within the town in order to defeat the invaders.
DMs looking to restrict Hoard of the Dragon Queen to a single adventure (possibly while running it as a D&D one-shot during a convention) can end the game with the "Dragon Attack" mission, where the players must wound the blue dragon attacking the village, causing the remaining raiders to flee. Those who wish to extend it can play through its remaining chapters, which should equal a few sessions worth of Dungeons & Dragons content.
Source: Dungeons & Dragons (1, 2), D&D Beyond