get specific column from a gridview

Question

hey guys, its me again lol.

anyway. my interface looks like this ... thats a sample interface that bugging me out. as i have 2 options.

option #1. enable the add button(button field) to get the value of the unit or serialnumber and insert it to a container table.
option #2. use select and the "add product to invoice" button (found below).

im not really that familiar with tinkering with the button field so im leaning more towards option #2. problem is im stuck with this property: gridview1.selectedrow.

i dont know whats next, is there a method that i can use to extract the value of a specified column?

thanks