I second everything big kusa says but will also add on some of my own thinking.
The more alien and foreign a setting or character is, the more exposition you may need to communicate the who, what, when, where and why. Stories featuring normal humans in normal situations from the perspective of normal humans doesn't need to explain where Europe is or what a McDonald's is. Familiarity can be assumed. The more unfamiliar a work gets the more you need to explain. It's the.gaps between "set in Atlanta," vs "set in a fantasy world where heroes are often reincarnated to do battle" vs "set on a desert planet dominated by massive, divine worms whose life cycle produces the lifeblood of the galaxy, a drug allowing enhanced mental faculties and precognition."
With that out of the way, writing normal characters is easy. You don't need to explain why Bob from accounting has a cup of coffee every morning. It's just his habit. Conversely, you may need to explain why he works in a cubicle across from Za'hathoriana, elven witch, whose byzantine laws dictate that she has to file multiple expensive pieces of paperwork every time she wants to create a magic wand with the BATFE (Bureau of Arcanists, Theologists, Farseers, and Evokers). I don't neee to explain how and why my main characters are rednecks, since that's the only kind of protagonist I write. I can assume my readers know what one of those is or they have an equivalent in their country (please send me a hot bogan babe, any aussies reading this). I do have to explain why one of them is an engineering student, why one of them is able to use magic, or why the other is an AI construct used as a hacking tool by down on their luck junkies.
A good rule of thumb is to ask what's unfamiliar in your work, and explain/show that. Then ask if it's necessary to the story, and pare anything thet isn't down.
You don't need to tell your audience what an elf is since most of us have consumed fantasy literature recently. Pointy ears, long lived, usually talented with magic, quite androgyne.
You do need to tell us if they're sexually dimorphic with the males being short and the females being tall, with very strict gender roles.
You don't need to tell us about their gender/sexual politics in a mystery thriller about a murdered merchant and the cadre of suspects ranging from elves to orcs to a sentient suit of armor.
You do need to tell us how that sexual dimorphism plays into his elven friend's potential motive, being a freakishly tall and androgynous male elf shunned by his society for his looks. Maybe he was jealous of his friend's good fortune and wanted some for himself.