The bar mark type is useful when you want to compare measures across categories, or when you want to break data down into stacked bars. Tableau displays your data using bars when:
The Mark menu is set to Automatic,
and you place a dimension and a measure as the inner fields on the Rows and Columns
(or vice versa). The inner fields are the fields furthest to the right
on the shelves. If the dimension is a date dimension, the Line
mark is chosen instead.
You select Bar from the Mark menu.
The data view shown below displays a dimension as the columns of the table, and a measure as the rows of the table. It is also color-encoded by a dimension (Department). Because the Mark menu is set to Automatic, data is displayed using bars.
To try some hands-on exercises for building bar charts, see Building Bar Charts.