Change the Symbology to depict demographic data on the map. Use the layer's Properties dialogue (right-click on the layer's name in the Table of Contents) and choose the Symbology tab. Quantities ... Graduated Color is often useful to visualize numeric data in ranges as a choropleth map. You will often want to normalize the value of a variable with a total for that geographic unit (e.g., divide the number of rental units per tract by the total number of housing units per tract to get a ratio).
Online help on displaying layers in general | Discussion of classification methods for graduated symbolization
