What the hell. are endnotes.?

I have this persuasive essay I have to write in that stupid MLA Format **** and I can't understand anything from any sites I just can't get what they're saying. Last year I did what I thought endnotes were and I got marked down so I asked my teacher what was wrong with them and she said they 'weren't proper endnotes' but she never bothered explaining what they really were. So now im **** out of luck this year pretty much failing english and I've gotta get it up. Help, and specific would be amazing thank you