Please give answer

Hi,

In selection-screen one parameter is there But we are not enter any value but We press f4 some window have to diaplay,

To do that in selction-screen in which event we have to write code and what code we have to write.

But we have to do that useing only code,We are not createing any serch help here.Useing only event in selection-screen.

Please give me answer.