I just killed the two ogres near what I believe is a lake, in the tutorial part. There's a boat that looks like a coffin and I can only "examine" it. If I do that the character jumps in and, after a loading screen, nothing seems to happen. What's the deal?
The boat changes the sex/gender of your character. If you enter it as male, you come out as female and vice versa. It doesn't change anything else about your character, so any hair/makeup/tattoos/body style/etc remain as before.
Since so much of your body shape is obscured by armor, the change isn't very obvious. Additionally, there are absolutely no known gameplay differences between playing as male vs. female, in the base game. If you have the DLCs though, there are certain armor sets that will give you hidden benefits if you're a certain gender.