ELI5: if matter can't be created or destroyed, how does matter currently exist? Isn't the existence of matter already breaking that law?

Matter can definitely be created and destroyed. Mass-energy, however, is preserved. Now if you want to go further with “then how was mass-energy created?” you’re getting into “Beginning of the universe” stuff and we don’t know how that functioned.

Bear in mind that a physical law doesn’t mean “Mother nature has to obey the speed limit” it means “We pretty much always see Mother Nature obey the speed limit.” It is an observation of how we see the universe functioning, not a limit we put on how the universe can function.

Explain Like I`m Five: good questions, best answers.