Fixed Spending includes the set of expenses you enter like housing, contributions to retirement and special expenses. But it also includes calculated amounts like taxes and Medicare Part B. 
To view a breakdown of fixed spending, view the Spending Overview report (as a table, not a color chart) and note that every column to the right of the first column (discretionary) and left of the last column (which is a total) is fixed spending. Fixed spending includes the OTHER column which combines all of your Special Expenses that you may have entered. 

See also this video: Reading Reports