If you've worked with Microsoft Excel or data in a tabular format before, you have probably pivoted data. Generally, you want to pivot data when it is in a cross-tab format to work with it in Tableau. While wide data may work well for reporting, data should be long when conducting the analysis. After you have connected to your data source, select multiple columns. Click the down caret to the upper-right of the column name and click the Pivot option in the menu:

The columns that you have previously selected will be pivoted. Always validate your data after you make any transformation; this will give you confidence in the results of the analysis. You can add or remove additional columns to the pivot in a similar manner – click the down caret of the field that you are interested in and follow the instructions: