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The dimensions are the information that you will drag and drop into the appropriate rows and columns.
If you click on the right part of the column name, a drop down arrow will appear. Click on the arrow and then go down to filter. Filter as needed.
When you first sort, the sum will be shown as ABC in the columns. To change, this move the Number of Records 
which is located on the left side of the screen to the Marks section. The Sum(NumbersofRecords) will now look like this - 
Click on the four dots to the left of it and chose the text option. Now the Sum(NumberofRecords) will look like this -
When you are completed with all the adjustments that you want to make, the final document will look similar to this -
Now, it is very important to just take a screenshot of the final data, open a blank document and save that screenshot. DO NOT SAVE THE TABLEAU DATA. This is because all of that information will become public, which we do not want since people's names are shown.