Adding dropdown in a grid column

Here I am stuck at one point. I added a dropdown in the grid column.
If I select any id in this dropdown related Description should be displayed in the Description column. I need this Solution. If anyone can aware of this please help me.

Can you please reply to this? If anyone aware of this issue?

What have you tried so far for filling that description. Typically that’s going to be a change event or something you use a BPM for on save. Couple ways to skin the cat.

I didn’t got the point… can you please brief it.