Oracle 12.1.0.1 Standard, create a user for a specific PDB.
C:\> sqlplus SYSTEM@oracle12
Enter password: ********
SQL> SELECT PDB FROM v$services;
PDB
-----------
MYDB
CDB$ROOT
SQL> ALTER SESSION SET container=MYDB;
Session altered.
SQL> CREATE USER MYUSER IDENTIFIED BY secret;
User created.
SQL> GRANT CONNECT, CREATE SESSION, RESOURCE, PDB_DBA to MYUSER container=CURRENT;
Grant succeeded;
SQL> commit;
Commit complete.
Enter password: ********
SQL> SELECT PDB FROM v$services;
PDB
-----------
MYDB
CDB$ROOT
SQL> ALTER SESSION SET container=MYDB;
Session altered.
SQL> CREATE USER MYUSER IDENTIFIED BY secret;
User created.
SQL> GRANT CONNECT, CREATE SESSION, RESOURCE, PDB_DBA to MYUSER container=CURRENT;
Grant succeeded;
SQL> commit;
Commit complete.