Display selected row data to the text box of other window.

Question

I have a DataGrid that have two columns PID and Process Name that dynamically displays running processes at run time.I have two windows. On the main window there is a text box and the browse button. When i click on the browse button the new window appears that shows all the processes currently running in my pc. I would like the program to display the data in the selected ROW to the textbox of main window.however I'm not sure how to get this data and display it in the text box based on the row that is selected.