The following is some basic, ABC information on aspects. An aspect exists between two planets when the angular distance between them is within a certain range, or orb, of closeness to certain numerical values. I've also listed the 150 degree aspect below.
Aspects are an absolutely crucial requisite for any thorough understanding of a birth chart.
Without aspects one could not fully understand the workings of a planet. There are typically three ways to understand how a planet will operate. Take the example of Venus in Pisces in the 3rd House conjunct Saturn, square Pluto, and opposite Jupiter. It is in Pisces. By its house.