There is no single answer to how all complex or rare words are formed, but words like the ones mentioned in your comment are often derived by combining affixes with word stems. In other words, they are pieced together from parts that carry existing meanings to create a new, complex meaning.
Though I know you're seeking a general answer, the best illustration is by example, so let's look at the second word you cited, antediluvian, defined as
of or belonging to the time before the biblical Flood.
This is made up of three parts, a prefix, ante-, a stem, and a suffix, -an.
To break it down, the prefix ante- as defined by Oxford English Dictionary means:
Preceding in place or position; usually referring to a smaller space entered before another (usually larger) one.
The stem comes from Latin, dīluvium, meaning "deluge."
The suffix -an can alter a word in various nuanced ways, but essentially it means:
of, or belonging to
So the word antediluvian means essentially, "Of or belonging to a time preceding the flood."
This formula won't always apply neatly to all rare or complex words, but if you approach such words by breaking them down into their parts, the derivation is usually more intuitive. To learn more, the best approach would be to pick certain words that interest you and search for their derivations in OED, or if you don't have access to OED, you can use Etymology Online.
If you take a look at the other example words you cited, you will notice that they also contain affixes and parts that have older meanings than the whole word. There is no singular social phenomenon by which the whole word is ultimately formed, but logic suggests that there must have been a "first use," so consider that a writer might coin such a word by combining meaningful parts and other writers might pick up the word until it rises out of obscurity to become an accepted part of the language. Or perhaps the component parts are so intuitively meaningful that the word could have been independently coined by multiple writers or speakers without knowledge of each other's uses -- ultimately, the end result is the same.
It's also worth noting that a "first use" or "early use" of such words built out of component parts might not be spelled the same as the eventually accepted word. Often a word might originally be made up of hyphenated parts and later be spelled without hyphens.