I am copying this verbatim from a post I found by Kevin Spencer which is the clearest explanation I have seen of the main properties of a DataGridViewComboBox. It’s here for my reference. Yay if it helps you too!
The DataGridView itself has a DataSource property that determines what columns are in it. The DataGridViewComboBox column also has a DataSource property, but that isn’t the same as the DataSource of the DataGridView. It is the DataSource that is used to populate the ComboBox in each cell. The DataMember and ValueMember properties are the column names of the columns in the ComboBox’s DataSource that define what is displayed in the ComboBox, and the underlying value for that item. It is the DataPropertyName property of the DataGridViewComboBoxColumn that determines the column name in the DataGridView’s DataSource that the ataGridViewComboBoxColumn is associated with. The ValueMember determines the value that will be set for that column in the DataGridView’s DataSource.
Here’s the original link. Thanks, Kevin Spencer.