It's likely about the adventures in the Sea of Thieves world. It might feature pirates, their quests for treasure, battles on the high seas, and the various strange and dangerous creatures that inhabit that world.
Yes, in a sense. Other players might take credit for things you've done in the game, like finding a valuable treasure or completing a difficult quest first. They could brag about it as if it were their own accomplishment, which is like stealing your story.