The easiest way to freeze food is to get a package of gallon-size freezer bags. Put food in them. Squish out the air before you zip the tops shut. Some people actually suck out the remaining air through a straw. Foods packaged this way can be rolled into tidy cylinders or frozen flat to stack.
Rigid containers are good for freezing liquids.
The square ones save space by stacking. If you don't, the next time you open your freezer you will discover a lid lying to one side and frozen soup protruding from the top of your Tupperware, where it is picking up objectionable flavors as fast as it can. In On Food and Cooking, Harold McGee explains that freezer burn is essentially a patch of freeze-dried meat on the surface of otherwise normally moist tissue. It happens to food that's been frozen awhile. Think of sublimation as the subzero equivalent of evaporation.