Proportion means making sure each of the parts are the right size to be correct for the whole. The best way to describe it is to imagine you are drawing a picture of a person. If you were drawing a person, the arms should not be too long or too short. It means making sure the head is not too big or too small for the body. That sort of thing.
In class, each student selected an object out of the still life bins and practiced drawing in proportion. They practiced doing basic comparison measuring to try to get the sizes right. Comparison measuring means that you 'measure' the short side with your fingers, and compare that to the other sides. If the short side counts as 'one', and the long side equals 3 of that 'one', you know to make it 3 times longer than the short side.
To work on this at home, select simple objects in the kitchen to draw. A pot or pan works great!