Hello In addition to the fields defined in CreateUserWizard i want to add some more fields to store information in database for some purpose.But could not get the way to execute the task.
You can Customize the CreateUserWizard markup as shown in the link. To store it in database you have several options depending on how you want to store it. Those fields won't be store automatically but you will have to do that manually.
Check these:
Storing User Profile into a Custom Table using CreateUser Wizard