if you don't understand russian, i'll tell you briefly what happened in this video.
everyone goes to computer class, but everyone focuses on chatting instead of the subject of the class. the girl got a chat message from some anonymous person who wants her.
the girl starts to speculate to herself who she got message from. she thinks about all the possible romantic encounters with her classmates. she also speculates that she has a lesbian secret admirer besides the boys at school, because why would anyone contact her anonymously.
but then finally the girl looked through everyone's screens to see if there were matching chat logs and then she went to her teacher and noticed that the teacher sent that message.