select statement

im developing invoice smartform.after giving invoice number in VF02 ,the user will go for print.how to write select statement for this in my driver program.for ex:in reports.we retrieve data by designing selection-screen using 'parameters' option.we pass this in select statement and get the data for particular invoice number.in smartform,how to code it in my program for particular invoice number that user gives it in VFO2.