The bit about the balloons in the first two pages no sense to me, so figured it wasn't worth continuing. When they were filled with air they exterted an upward

The bit about the balloons in the first two pages no sense to me, so figured it wasn't worth continuing. When they were filled with air they exterted an upward force on the spring? Why!? And then when the air was removed, the force was downward? By "air" did the author mean "helium" or something? Or are we underwater or on Venus or something? Also the meaning of "release" was poorly defined. Like... just draw me a free body diagram so I can tell what you're trying to say.