How to implement drag-and-drop from a list of items outside the layout?

[adhamenaya]

I have in my application a grid layout and a list of items. I want to allow the user to drag one of these items from list that is not part of the layout and drop it into the grid layout.
I'm not sure where to start with this implementation. What are the key steps that I need to follow to make this work?

Any help or guidance would be greatly appreciated. Thank you!