When something is in the 1st person, the main character(s) are explained with terms like I, me, and myself In these structures the main character's descriptions explain the story To the reader

Example "I passed through the closet door to retrieve my gear, and give Spike a cookie"

When something is in the 2nd person The main character is You thus most of the things that the character does and sees in the area are things that you see.

Example "You walk through the door way, and see everything cleverly organized in the shelves, it does not take you long to find your gear, and the cookies you set out to retrieve for Spike.

Its an easy mistake to make, both points of view are used a lot to describe what happens during a role-playing scenario. And when you read words that say "I" it is still pretty easy be put into in the position of the main character.

But if the dialogue sounds like someone else telling you what happened to them once, instead of you, yourself gathering info about the situations in the story then it isn't a 2nd person story, its a 1st person story.

I don't know how many people are familiar with Dungeons and Dragons, but I will use it as a metaphor until I think of something better.

It's the difference between hearing another player announce what they are going to do, verses hearing a Dungeon Master explain to you what you find, and what you find.