Sql Server Reporting
Dataset parameters are not defined there. 

To define the "value" of the parameter, you have to edit the dataset itself. That's where you will specify what value you want your query to run with; you can use a static value, or a report parameter. 

If you use a report parameter as the value for your dataset, the dataset will not execute until the report parameter value is defined by the user. This will make the report behave like, "the values of parameter 2 only become available after selecting parameter 1". 

Hope it helps.