Visual basic can be used for server side scripting. A component designed with Visual basic will not have any user interface instead provides the functionality of Active X to other programs via COM. This form of technique allows server side functionality and add in module.
RDO is Hierarchy model where as ADO is Object model. ADO can access data from both flat files as well as the data bases. I.e., It is encapsulation of DAO, RDO , OLE that is why we call it as OLE-DB Technology.
User defined functions can be created into the Microsoft spreadsheet. Spreadsheets can be customized according to the user needs by using VB applications. To create visual basic functions useful for spreadsheet you need to click Tools and select Macros where you will need to click on Visual basic editor.