Not very. Since quite obviously you know something about linguistics, I think you'd benefit from looking up descriptions of how English articles are used in grammars...
Some general remarks:
In general, the definite article means that the listener already knows what specific entity or entities you're talking about. This is easy to notice when something is introduced and then recalled: "I went into the room and I found a bunch of books and a couple computers. The computers looked pretty new."
Because this use depends on what the speaker assumes of the listener's knowledge, cultural factors are also relevant. If something is culturally understood to be normal along something else, it may be readily used with the definite article without any introduction: "The party was great, I especially loved the music" (music is very normal in a party). This is especially common when talking about parts: "I bought a new desktop computer but I still have to buy the keyboard that will go with it.", "I heard the song and I mostly loved it except for the beginning".
If these "parts" were weird, you'd need to say something like "The party was great, and there was even music, which I really loved", "I brought a new desktop and I'm thinking of buying a keyboard for it too". A more natural example: "We stood in a minute of silence while a trumpet played a mourning tune" (if listening to a trumpet was the normal thing to do during a minute of silence, English speakers would likely say "We stood in a minute of silence as the trumpet played").
"The" can sometimes imply that there's only one clear choice for something. For example, when conlanging, if a language only has one past-tense marker, you can generally refer to it as e.g. "(with, adding, by means of, via, lacking) the past-tense marker". However, if there are two or more past-tense markers, then the phrase "past-tense marker" is a category where there is more than one choice: "(with, adding, via...) a past-tense marker" (maybe any past-tense marker, or the one we're talking about at that moment).
Besides this, proper names typically don't take the definite article, unless they're modified by an adjective, relative clause or other modifiers to identify them as very particular. "the classic J.K. Rowling we all remember vs. the new J.K. Rowling", "the Taipei devoid of trees we used to know", "the Xwtek of today, not the Xwtek of yesteryear".
Abstractions when talked about as quasi-eternal concepts ("love", "hatred", "friendship", "curiosity"...) typically don't take any article even when modified: "indifference towards one's neighbour", "love for hockey", "Juvenile love always seems too intense in retrospect." If you use the definite article with these, then you're talking about an instance of these concepts, usually in the form of the ambience of a situation: "We could all perceive the curiosity driving them forward."
Beyond this, there is a lot of little details to know, often stuff that is special about certain social contexts, groups or communities...
For example, as you saw in the Language Practice thread, in the realm of Biology it's normal to use the definite article with a singular when talking about a species ("Thus the giraffe manages to graze on thorny trees."), even though the normal thing to do is to use the generic article-less plural ("This is how giraffes manage to feed on thorny trees.").
For another example, definite articles are often omitted in newspaper articles, source code comments and version-control entries (in a comment describing what a function does: "Return session type.", instead of "This returns the session type [of a user session passed in].").
For yet another example, older speakers sometimes use the definite article with the proper names of tech services or simply the names of technological devices ("This is the perfect spot for you to put on the Vine"), which has led some younger speakers online to use it rhetorically too (to express luddism or concerns about technology, to say things as someone who's not familiar with a service/device at all in a bit of a funny way, to make fun of older people, and various other purposes).
For one last example, the definite article can be used with a common noun to name places, often producing a medieval or early modern connotation. This is why the land of Tolkien's hobbits is called "The Shire", and why you may come across the likes of "Ye Olde Shoe Shoppe" ("The Old Shoe Shop", where "y" is an old variant of "þ", the letter thorn).
