Start with a simple 2x2 table, percentaged in the right direction. The INDEPENDENT variable is across the top and the DEPENDENT variable is on the side. We percentage down — within categories of the independent variable. Then we can compare across: "half of the boys have only a high school education compared to 30% of the girls."
How do we name this table? The convention will be "Dependent Variable by Independent Variable" so here that would be "Education by Sex."
What chart do we make to visualize this table? In fact, it's really too simple to need to be shown in a chart, but for the sake of illustration we continue. The relevant comparisons here are boys to girls. Two possible charts come to mind:
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Visually, proximity determines what comparison we do first. Since the first comparison in the 2x2 table is "50% of boys have HS compared to 30% of girls have HS," the chart on the left is the correct one here.
Let's look at it's components
needs more by way of summary and consideration of how this generalizes to other charts