Dont create reports in crystal report by the wizard, infact do like as blank report and then after selecting data source select the add command, then in ur command insert ur query and any place where u are using a where clause , on the side u will see add paramter, so add a parameter and then where u are using the where clause like see
select * from user where user_id={?id}
this id was the new parameter added
select top {?val} * from user
here val is the parameter
after creating the report in the programming, i mean in dotnet
create a text box for the value of the parameter and then, on a button click event write the following code

CrystalReport1 cr=new CrystalReport1();
cr.SetParameterValue("id",int.Parse(textBox1.Text));
crystalReportViewer1.ReportSource=cr;

this can be accessed by the index number also like by 0, 1 , 2
hope this will be useful