If you want to use the Embedded PL/SQL Gateway (EPG) to front APEX, you can follow the instructions here. 

SQL> CONN sys@pdb1 AS SYSDBASQL> @apex_epg_config.sql <passing in the base directory of the installation software as a parameter>

Check the port setting for XML DB Protocol Server.

SQL> SELECT DBMS_XDB.gethttpport FROM DUAL;

GETHTTPPORT

-----------

          0

1 row selected.

SQL>

If it is set to "0", you will need to set it to a non-zero value to enable it.

SQL> EXEC DBMS_XDB.sethttpport(8080);

PL/SQL procedure successfully completed.

SQL>

APEX should now be available from a URL like "http://machine:port/apex".