Is there a difference in addressing someone politely and casually in spanish?
Yes. The tu form of conjugation is used for people with whom you are comfortable. The Ud. is reserved for people of high esteem (such as professors).
How does one best prepare for a test they must take in only a few days?
Repetition. Whether it be done via flash cards, hand written notes carried in one's pocket, or a typed up study guide the repetition of the most important material for that test is what will most readily secure a workable grade at minimum.
In what way does Jung's teachings of "the shadow" pertain to our everyday lives.
Jung proposes that the shadow is the part of ourselves that we repress. In this way we may create stress for ourselves daily by repressing things that we believe we are not to interact with about ourselves.