In the original recording, this song is tuned a 1/2 step down from standard tuning. Marty teaches it in standard tuning however to make things easier as you are more than likely in standard tuning at the moment. After you learn the song, you can tune your guitar a half step down and try it again. Follow this link to learn how to tune your guitar a 1/2 step down.
Where Did You Sleep Last Night Guitar Lesson
As Performed by Nirvana