https://kb.tableau.com/articles/howto/filtering-data-with-a-parameter?lang=fr-fr After creating a parameter named Choose Region, you want to use it to filter the chart based on the user's selection. To do this, you would create a calculated field with the formula [Region] = [Choose Region] and add this calculated field to the Filters card. This will dynamically filter the chart to display data only for the region that matches the user's selection in the Choose Region parameter.

You can create aliases for the members of a dimension by right-clicking the dimension in the Data pane or in the view and selecting Aliases. This changes how the values are displayed in the view, but not the underlying data. For example, you can create an alias for "Central" as "Midwest".
In Tableau, aliases can be used to change the way dimension members appear without altering the underlying data. This is useful for display purposes and does not create a new field within the dataset.