query parameter

Hi RashmitaR,

You can image that the query parameter is a bridge. Users can check different values for the parameter, then other object accept this value and perform a set of operation which has been configured with query parameter. If you are familiar with T-SQL or SQL Server Reporting services, it's easy to understand how it works.

In addition to ankitpatira's comment, you need to note some settings in the sample report. You can see there is a query parameter named Country. And the author uses this parameter to filter the Country field. 

As the parameter has a list of values, we can check prefer value when open the report, then the value is passed behind the scene to filter Country field. I wonder you can know how query parameter works in this scenario now.

Certainly, we can use query parameter in another ways. You can take a look at those articles to learn more:

Creating M Functions From Parameterised Queries In Power BI
Power BI Desktop Query Parameters, Part 1

Power BI Desktop Query Parameters, Part2 – Dynamic Data Masking and Query Parameters

If you have any question, please feel free to ask.

Best Regards,
Qiuyun Yu