Bishal,
I have put the links because you ask about "
How do I execute DDBB creation script?" i don't know if you have done the steps
The first link if for create databases, the second to see different ways to do (manually, using wizard,...) the last link because is in the the steps to configure databases.
If you have created the databases, then you need to check why is not connecting to databases (Message error suggest the problem).
Have you review the logs after the error?
regards