mpMS:thanks for the immediate response. I would like to rephrase my question. I wanted to create an account that will be db_owner of specific database
After creating your login, do the following
1) Ensure that the login is a user of the database. Go to the User folder of your database and add the user. You can find the User folder in the Security folder of your database.
2) There, you should specify the newly created login. You can browse for it if you want. Then check the role in the lowermost checkbox to which this login should be a member of. You can see the role "dbo_owner" there.
Be aware that in order to do this, you must have high privileges in the database. If you are a local administrator of the database, there's no problem because accounts in the Administrators group is mapped to the dbo schema and that means you also own the database. The safe practice is to create a database using local administror account.