This might be a good start for you
https://warcraft.wiki.gg/wiki/HOWTOs
But, sometimes, it's worth finding a simple addon and finding out what makes it work and use that as inspiration.
My first addon was a simple Loot Alerter that allowed me to tag item types etc I wanted to know about and the moment something was looted that matched that filter it would display a message.
However, I did have the advantage of previous programming knowledge. So perhaps someone who wasn't could offer their words of wisdom.