Before getting into the specific buttons and what each one does, it’s worth understanding the bigger picture: what actually happens when you make a change and want your users to see it?
Your app checks in with AppNatively
Your app doesn’t carry its screens, text, or design permanently inside the file your users installed. Instead, it checks in with AppNatively and loads all of that fresh, each time it opens.
That’s why publishing is usually the whole job
Because of that, hitting Publish is normally everything you need to do. Your users see the change the next time they open the app – no app store review to wait through, no update for them to download, no delay.
The one exception
Once in a while, a change needs something the installed app itself doesn’t have yet – a capability only a newer version of the app can provide. When that happens, AppNatively tells you right away, rather than letting the change silently fail. See When a new release is required for exactly what that looks like and what to do about it.
Bottom line
Instant updates are the rule. A new store submission is the exception – and you’ll always be told clearly when one’s needed, rather than having to guess or find out the hard way.