Assuming that you're using an rdlc report in local processing mode & using winforms,
(You need to be more specific with these things)
Here's an example on how to add parameters:
ReportViewer1.LocalReport.SetParameters(new Microsoft.Reporting.WinForms.ReportParameters[] { new Microsoft.Reporting.WinForms.ReportParameter("ParamName",YourValue)})
Where ReportViewer1 is your ReportViewer, ParamName is the name of the parameter
To see the list of parameters in your report, open your report, right click on it & click on parameters.