In SSRS, parameters are used to provide dynamic values to a report. They can be set in the report's dataset queries, as well as in other parts of the report such as filters, expressions, and data regions.

When you set a parameter in a dataset query, the parameter is used in the WHERE clause of the query to filter the data returned by the query. The parameter's value is passed to the query when the report is executed, and the query uses that value to filter the data.

To use a parameter in a dataset query, you need to declare the parameter in the query, and then use the parameter in the WHERE clause of the query. For example, if you have a parameter named "rundate" that you want to use in a query, you would declare the parameter in the query like this:

DECLARE @rundate datetime

Then you can use the parameter in the WHERE clause of the query like this:

WHERE some_date_column = @rundate

It is not necessary to initialize the parameter before you use it in the query, as the parameter will be passed a value when the report is executed.

Regarding the problem you are having, it could be that the remnants of the previous content you added and deleted are causing conflicts in the code. It's also possible that there is an issue with