In the Lord of the Rings, what is the explanation for swords and other metal goods?

At some point in the past, the arts of smelting, smithing, casting were discovered, refined over the centuries, different races and cultures advanced them in different ways, and eventually led to swords, within shirts, magic rings, etc.

Same thing with star wars, in-universe they have tens of thousands of years of history, I think canonically the old Republic was founded 25-or-so thousand years ago, if you go back that far in real earth human history and you’re pretty much at the point where a handful of weird wolves are starting to get comfortable enough with humans to let us start domesticating them.

And at that point in the star wars timeline, space travel and other advanced technology is already pretty well-established, so there’s probably at least that long again of incremental technological advancements leading up to that point.

Basically they just got a massive head-start on us

As far as how and where the technology is made, we get little glimpses of it here and there, droid factories on Geonosis, corelian shipyards, various mechanics, scrapyards, tinkerers, etc.

But that’s all just kind of backdrop. Star wars is a space opera adventure thing, not a mockumentary about the history of lightsabers and hyperspace drives, or a how-its-made for blaster pistols and gonk droids. It wouldn’t make sense for most star wars media to really go into depth about that kind of stuff and probably would piss people off if they did (not that most star wars fans don’t exist in a perpetual state of being angry at star wars about something anyway)

You wouldn’t go into a Fast and Furious movie expecting a whole history and mechanics lesson on automobiles, the movies are focusing on a handful of people who (race cars? Fight terrorists with cars? I really don’t know I’ve actually never seen any of them) there’s a whole in-universe world around them where all of those things happened/are happening out of sight and out of mind but it’s not directly relevant to the plot so it gets kind of glossed over, you can just assume most of the history and engineering stuff has been handled by people somewhere off-screen at some point in time.

Same with star wars, there’s untold trillions or more people scattered across millions of inhabited planets working dead-end jobs making widgets that have built on millennia of science and technology, but the stories focus on a handful of freedom fighters, smugglers, soldiers, warrior monks, etc. who mostly just use those things and probably don’t have much more idea how their hyperdrive works than you do about the alternator in your car.