Two or more planets that are almost in the same place in your chart (within approximately 4 degrees from each other) are in Conjunction. This means they affect each other very strongly, usually blending and assisting each other. 

When planets fall exactly across the circle of the chart from each other, this is called Opposition. Planets in opposition pull away from each other causing tension in their relationship to each other, indicating a polarity. 

Planets at a 90 degree angle from each other are said to be Square. Squared planets are often difficult to manage, causing tension but also "building character." 

A Trine is when there is 120 degrees between the planets. Three planets in Trine create a triangle together. This is a helpful relationship, bringing ease to a person's life. 

Like Trines, Sextiles, at 60 degrees apart, bring pleasant characteristics to a chart.