Single-series bar charts are represented by rectangular horizontal filled areas starting from the vertical baseline. They are all using the same color, unless you opt for negative values with two alternate colors.
Our US Sales demo charts show totals of product quantities sold in US in three different years. The single series is the US country, and the values for each year are 2007, 2008 and 2009. Remark the vertical X axis is a category axis: year values are distributed at equal intervals on the axis. All year bars have the same color, unless you also use negative values with alternate colors. Our bar charts look like horizontal histograms, because they show data of the same kind (i.e. product quantities). Unlike histograms, bar charts display often different categories for each point.