Conjunctions (0 degree angles) can go in either a positive or negative direction, depending on the nature of the two planets coming together. For example, Venus and Jupiter make a fun-yet-lazy conjunction, while Mars and Pluto can be heavy, since they both relate to anger and ego.
Planets in conjunction with one another typically share the same house in your birth chart. They operate as a pair, and go hand in hand.
Aspects are angles created by the varying positions of the planets in the sky in relation to one another.