The Skull and Bones closed beta is on now. If you have an invite and some time to launch your pirate adventures, Ubisoft has some guidelines and advice on what you should know about the beta.
Skull and Bones has been delayed a number of times, leading to some casting doubt over the game, but this closed beta is not under NDA. If you browse over on Twitch, you'll see a number of streamers sharing their beta sessions and get an idea of what the game is like in its current state.
The Ubisoft team is also streaming, and they are giving away closed beta codes. The beta itself runs through the 28th, so you still have the full weekend to get in there and become a pirate if you're lucky enough to score an invite.
As for the beta, you'll be able to sail around and explore the red aisle and the coast of Africa and you'll be able to take on some of the campaign mission contracts, and reach the maximum beta rank of Buccaneer.
Since anyone who has a beta code can also invite up to two friends to join them, you can choose to play solo but if you have two buddies to invite, you can also play entirely co-op. this means you can join your friends to sail around and seek treasure, and even to play through and complete contracts. If you are playing in co-op mode, the difficulty will be scaled up, and as a result, so will the loot. This is also something to keep in mind for when the game does launch, because co-op will be the more rewarding path if you choose to play that way.
You'll have access to an in-game journal to track your journeys and your contracts, side quests, and of course, treasure maps. Since you are a pirate with important things to do, your crew is designed to be helpful. They'll warn you about a ship in the distance, supplies they spot floating around, dangers, or issues with the ship itself. You can also just ask them to sing you a nice sea shanty.
Check out the full beta devblog at Ubisoft.