Filters Whith Diferent Values (parameters)

I want to make a filtering by using a string parameter (a,b).
The initial result of my query is this:

Name Letter
Luis a
Juan b
Michel c

Note: There are 2 columns (Name) and (letter)

So after filtering the result pane should be like this

Name Letter
Luis a
Juan b

If i send a diferent filtering parameter (b), the result should change like this

Name Letter
Juan b

How can I do this??

Thyanks