I have 3 TextBoxes and 1 Button and want to enter each of the the TextBoxes data into a ListBox in separate columns.
As Ray correctly points out, ListView will do the job. However if you're stuck with and/or want to use ListBox you can also use an ItemTemplate with Grid and set the Grid.IsSharedSizeScope property on the ListBox itself. For example:
This is a neat trick which can also be applied to other cases where you have multiple instances of Grid (ie: one per ListBoxItem as per this case) and want to share a column.
Best regards,