1.Now i want to delete the "testdb" which i have crteated and used the wrong paswd (as it contains @)...Why you want to delete the entire db? Why don't you just change the password?
2.suppose i want to create a new user apart from hr ....what steps shud i follow...In the documentation at http://tahiti.oracle.com , search for the command create user . It would tell you the steps.
3.does hr user has all rights to create update db tables/schema etc .....Any user by default has no right, not to even connect to the db. You would have to assign the permissions to that user to make him do whatever is needed for him.