Hey, Teri! Welcome to GT. ZZSmilieZZ

Originally Posted by: zenbuddhette
I am trying to understand [u]why[/u] the 1, 4, 5 system works for determining major chords for each key. Can you provide more insight, please?

Great question! This tutorial covers that topic in detail.

https://www.guitartricks.com/tutorial.php?input=495

These tutorials cover the basic practical applications of the theory.

https://www.guitartricks.com/tutorial.php?input=426
https://www.guitartricks.com/tutorial.php?input=427
https://www.guitartricks.com/tutorial.php?input=428

Hope this helps! Please ask more if necessary & best of success!