Issues with grid-row property

I don’t understand how grid property works in the grid section. In the exercises mosh set the grid-column property to 2/4 and the row one to 1/3. It means that the image takes up the second cell untill the fourth one? it is not clear at all. the third image is placed in the the third cell. Could anyone just explain me how it works please. I am really confused.

In chrome you can turn on the row labels to see the number of each row.