Creating functions and triggers

Is there a good, hold your hand type of tutorial or howto on creating
functions and triggers and using them together? I'm learning PostgreSQL
after spending years with MySQL and the information at
techdocs.postgresql.org - while good, is a little deep for me right now.
Specificly I would like to be able to read something that will tell me
how to create a function that will can run a shell script when certain
words are entered into a record. Thanks for your time and guidance.

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