There exists a generic system to show users that an action was performed successfully, or more importantly, failed. This system is known as "flash messages". The screenshot below shows the various severity levels of messages that can be emitted.
The different severity levels are described below:
Notifications are used to show very low severity information. Such information usually is so unimportant that it can be left out, unless running in some kind of debug mode.
Information messages are to give the user some information that might be good to know.
OK messages are to signal a user about a successfully executed action.
Warning messages show a user that some action might be dangerous, cause trouble or might have partially failed.
Error messages are to signal failed actions, security issues, errors and the like.