After installing 12c database, you may want to enable dbconsole just like 10g and 11g, but in fact, there's no emctl command to operate with. This is because 12c uses EM Express version instead of dbconsole. It's enabled by default.
Before accessing EM Database Express 12c, you have to make sure which port is used.
SQL> select dbms_xdb_config.getHttpsPort() port_number from dual;
As you can see, Port 5500 is set for EM Express 12c. Actually, 5500 is the default value. If the result is empty or undesired, you can use the following function to change it.
SQL> exec dbms_xdb_config.sethttpsport(5500);
Now we can connect EM. Let's see the format of connection URL:
https://<IP Address>:<Port Number>/em/logon
As a DBA, you can logon the GUI as sys or system. But for others like system operators, you can give them a specific user account with basic privileges to logon EM Express.
SQL> create user embasic identified by <password>;
SQL> grant connect to embasic;
SQL> grant EM_EXPRESS_BASIC to embasic;
Note: EM_EXPRESS_BASIC is a role.
Express version of enterprise manager is bundled with database software and very handy to use but very limited in functions, compared with grid control or cloud control 12c which are separate products in Oracle and should be running on standalone machines.