How to Pass Text Box from Child To Parent Window

Question

Hi, I am Using One Master Page and That is Linked with  one Parent Window when I Click the Link Button in the Parent Window, The Child Window is Opening and I am picking the Grid View Cell Value into the Text Box of Child Window. Now i want to transfer the Picked Text Box Value of Child Window  to Parent Window Text Box and The Child Window Need To close By Clicking OK Button on the Child Window
 
Can U Help?