Linear functions have a constant rate of change (slope) between any two points. The document provides methods for determining if a set of data represents a linear function, writing the equation of a line given various parameters like slope and intercepts, and properties of lines like parallel, perpendicular, vertical and horizontal lines. It also discusses how to find the equation of a perpendicular bisector by calculating the slope, midpoint and using the negative reciprocal slope in the point-slope form.