I am glad my blog helped - all I did was read the instructions in the Install Guide and follow them ;-)
[root@localhost ~]# dbca
bash: dbca: command not found
If you were able to invoke runInstaller to install Oracle, you will need to follow similar steps to invoke dbca.
First, never log in to your server as root - it is a definite way of hosing/trashing your server, most likely by a careless or incomplete command. Except for running "root.sh" after an Oracle install, Oracle software does not need root privileges - ever. Always log in to the server as the owner of the Oracle binaries (typically oracle).
Second, before invoking any Oracle executable (like dbca), required environment variables need to be set - these are documented at http://docs.oracle.com/cd/E11882_01/server.112/e10839/admin_ora.htm#i46652. At the minimum, you will need to set ORACLE_BASE, ORACLE_HOME, ORACLE_SID, PATH and TNS_ADMIN. If you were paying attention to my blog article that you followed, you would have noticed them :-)
For executing dbca, pl see the steps at http://docs.oracle.com/cd/E11882_01/server.112/e10897/install.htm#BABBBHJB - do not set (i.e. unset) ORACLE_SID before executing dbca.
Log in to the oracle account on the server (log in directly, do not "su" via root), set the ORACLE_BASE, ORACLE_HOME and PATH variables, navigate to ORACLE_HOME/bin directory, then issue "dbca" command.