During the Ubisoft Forward presentation, Skull and Bones: Worldwide Gameplay Reveal, it was confirmed that you aren’t restricted to playing co-op with other people. You can still do that, of course, but you can also play solo.
More specifically, in a post from Xbox Wire, it's noted that:
"You can play Skull and Bones solo, or team up with two other players — or enable PvP battles to see who is the most ruthless pirate. Skull and Bones is a live-service game, and each season will bring new content, contracts, and challenges."
The news that Skull and Bones can be played solo is exciting to hear, as Ubisoft has confirmed that Skull and Bones will indeed be a live-service game, and one that looks like it'd be a lot easier to navigate with the help of others.
In terms of what sort of gameplay you can expect from Skull and Bones, it's centered around the player starting things off on an island as the survivor of a shipwreck.
With the ability to craft a small ship, players will need to put together a crew and gather resources in order to gain Infamy and become the biggest, baddest ship on the Indian Ocean at the end of the 17th century "during the Golden Age of Piracy."
For more on Skull and Bones, be sure to read through some of our other coverage including the release date for Skull and Bones.