QUESTION: how does the update actually work?

[itsmenewbie03]

I tried implementing a self update feature on my project but ended up reverting it as I can't seem to see how it does the update?
I was able to complete the setup but for some reason the getAvailableVersion does not return the latest release but it does reflect if I use the getReleases function. I tried reading the readme over and over but no luck still I don't understand how it does the self update.