As stated in the game's FAQ, this beta includes the first few levels of the game, but any progress made in this beta will not carry over into the full release. Multiplayer in the beta is done through Xbox Live. The beta will last around 2 or 3 weeks.
Dungeons is Mojang's RPG action-adventure twist on Minecraft, and is the company's second time expanding on the base game, after their mobile AR game Minecraft Earth which entered early access last year.
Minecraft Dungeons can be played with up to four other players who will complete challenges and quests in a procedurally-generated world as they proceed through the game, and features many new gameplay elements not seen in the base game. The main antagonist is called the Arch-Illager, and must be defeated by the players.
The game was announced at Mojang's live Minecon Earth stream back in September 2018, and will be releasing this April. If you signed up for the beta, make sure to check your email as you may have received an access token to the game.
Upon release, the standard edition of the game will cost US$20, with the Hero edition costing $30 and including some cosmetic items and two DLC packs. The game will also come to the Xbox Game Pass on PC and Xbox One. Even after release, the game will continue to receive free content updates.