Hi Pravat,
It seems you use ASPX templates. If so, you can add user control directly to appropriate ASPX template e.g. using Visual Studio. If you want to be able to add web parts in 'Design' tab in CMSDesk, you will need to use Portal Engine instead. Please see '
Portal templates vs ASPX templates' and related topics in the same section for more details.
Best Regards,
Martin Dobsicek