You create a visualization by first adding a measure to rows.

In Tableau, when you initially add a measure to the rows shelf, you create one mark in the view that represents the aggregate value of that measure. When you then add a dimension with 11 members to the columns shelf, the view is subdivided into 11 separate marks, each representing the measure for one of the dimension members. This results in a total of 11 marks in the view after the dimension is added, one for each member of the dimension.