You have to be subtle describing a protagonist in first person. They can tell us the color of their hair and eyes when it pertains to actions/events in the story. They can compare their height to another person. They can pick out clothes so we know what they're wearing.

One thing I've heard that's a no-no is having them look at themselves in a mirror and addressing their features that way.

Second person is where the story is written in a fashion that sounds like the "narrator" is talking to the reader.

"You" see her running down the street. She turns left on Elm and heads down to the corner before she stops.