how to modifying a single cell ina grid in udt

Got a problem I hope someone can assist me with. I have a custom program generating an editable grid

I can add and delete column with events, but how can i modifying cell by cell?

Any thoughts would be greatly appreciated. Btw, my knowledge of OO is passable, but not great, so any explanations of what the code is doing in a proposed solution would be greatly appreciated.

thank you