Select exactly two Y columns.
Select required data.
Select Plot > Statistical: Population Pyramid.
This is a two-layer bar graph, which can be used to present the population pyramid about males and females at a certain year. So, by default, the two data columns should contains the population numbers of the male and female respectively.
The vertical axis shows the age groups which are always age ranges, such as 5-9 years; the horizontal axis shows the population of each age range.