There are three common perspectives used in writing: Third Person, which only refers to characters from an outside point of view; Second Person, which refers to a main character as "you"; and First Person, in which the narrator is a character referring to themselves as "I". AI Dungeon is capable of using all three, though it will default to the Second Person perspective.
Second Person is the default prompt perspective. All of AI Dungeon's default scenarios use this perspective. The player is referred to as "you," and commands are entered into the Do button as if the "You" is already there. e.g.
>put the hat on the cow.
Using the Say command will append
>You say: to the beginning of whatever dialogue your character says, and a quotation mark to the end if one is missing.
The Story command allows the player to take control of the story without directly controlling their player character. This allows the player to lead the events of their story in a direction of their choosing by causing the other characters in the story to do an action, or causing something else to happen within the story's world.
In the third person perspective, the Player character is referred to by name or their pronouns, not "you." This is the default perspective in multiplayer sessions.
Third Person is also used by players who wish for their stories to have a more traditional "booklike" feel, instead of the choose-your-own-adventure feeling of Second Person. There are some known quirks with this mode, because the AI was mostly trained to play in Second Person mode. Avoiding inputs written in Second Person and being careful to avoid references to "you" in particular can help maintain Third Person mode, but if the AI makes a mistake and slips into Second Person by mistake, Altering out or Retrying will usually bring things back on track.
Use in Multiplayer
As mentioned above, Third Person is used by default in multiplayer. The Do and Say commands are replaced with Third Person-specific commands that contain the players' character's name. e.g.
First person is not officially supported by AI Dungeon, and is NOT recommended to newer users because of this, but it can be done without much hassle. As the AI adapts to the player's writing style over the course of a story, enough messages using First Person pronouns such as "I," "me," "my," and "mine" will cause the AI to quickly adopt this storytelling style and use it for the rest of the adventure.
To get a game to go into First Person at the beginning, use Alter to edit the prompt, replacing all second-person words ("You") with first-person words ("I"). You will then need to use story inputs exclusively, and occasionally need to use Alter again if the AI gives you a message with second-person that you otherwise like. Remember that Remember must also be in First-Person, and that any World Info referring to "you" is going to get messed up.
Playing as Named Characters
To play as a character named in the World Info, all you need to do is refer to your main character as them. In Third Person, this is as simple as using their name. In second and first person, this is as simple as saying "You are [NAME]" or "I am [NAME]" respectively. The AI will pick up on the idea that this is referring to your character surprisingly well.