The labor theory of value is the idea that the value of stuff comes from the average amount of work required to make/get it.

So like gold being scarce takes more labor time because you spend a lot of time looking for it, and then a lot of time refining it once you do find it which makes it more expensive and like modern agricultural techniques mean a bushel of wheat takes less labor time than ever and is thus cheap.

The labor of learning to do/make the thing is part of the labor time involved in the thing, so if it requires a lot of training to do, it’s more expensive.

Labor is defined as socially necessary labor: meaning that the average amount of time required to do/make the thing is what counts which is why dolls assembled by takes-way-too-long-assembling-dolls-Bob aren’t more expensive than those assembled by really-speedy-at-a-assembling-dolls-Pat.

Also socially necessary labor is determined by how much of a thing society actually wants which is why no matter how many hours you spend making a statue of Elvis out of cow manure you probably won’t get paid anything for it because society probably didn’t want that and never will.

Incidentally the socially necessary labor thing is also why Ralph Lauren t-shirts cost four times the price of a normal t-shirt, because society has decided that the labor of many highly trained professionals creating and maintaining the idea of Ralph Lauren is something they want and so that labor is socially necessary weirdly.

Also when society makes too much of something the price temporarily drops below its actual value and when society makes too little it rises above its actual value but that’ll correct itself.