1. Login as sysdba in oracle developer.
2. Execute the create user statement. For example, create a new user named smith with a password of password as follows:
   CREATE USER smith IDENTIFIED BY password;
3. Grant specific access to the new schema user. For example:
   GRANT CREATE TABLE TO smith; (Or this one to give all privileges to this user )
   GRANT ALL PRIVILEGES TO smith;
4. Verify schema creation. For example, use the following query for new user smith:
   SELECT username, account_status FROM dba_users WHERE username = 'SMITH';
5. Then login as smith

https://stackoverflow.com/questions/33527917/i-am-trying-to-create-new-schema-in-oracle-sql-developer