This is the third chore assigned to you by Nancy, after you have completed the first two (Clean my room and Brush my teeth).
What to do?Edit
You must go to the kitchen and open the counter doors under the sink to find the trash bag. Take it and go out into the courtyard, beyond the toolshed and lay down the bag before the dumpster. Manually open the top of the container and, using telekinesis, drop the bag inside.
In version 1.0, this chore becomes available in the second chapter but you cannot complete it untill chapter 4 since the door to the courtyard is locked. In version 1.02.3866 however, Nancy will not give you anyother tasks untill chapter 4, making it impossible to obtain the ouija board earlier.