the people who, the book that, whose: joining sentences like a native
Spanish que covers English who, which AND that — for people and things alike. It can never be left out, unlike English "that".
La chica que vive arriba es médica. (The girl who lives upstairs is a doctor.)
El libro que compré es buenísimo. (The book [that] I bought is great.)
English drops "that" (the book I bought); Spanish never drops que. El libro que compré — always.
For people after a preposition, use quien/quienes (or el que/la que). Bare que alone won't do after con, para, de...
El amigo con quien viajé... (The friend with whom I travelled / the friend I travelled with...)
La profesora de quien te hablé... (The teacher I told you about...)
English hides the preposition at the end (the friend I travelled WITH); Spanish puts it FIRST: con quien, de quien, para quien.
After prepositions — and for "the one who/which" — Spanish uses el/la/los/las que, agreeing with the noun.
La empresa para la que trabajo es alemana. (The company I work for is German.)
Los que llegaron tarde no entraron. (The ones who arrived late didn't get in.)
Pick the article that matches: el barrio en el que vivo · la casa en la que nací.
Lo que = "what" in the sense of "the thing that". A hugely common connector.
No entiendo lo que dices. (I don't understand what you are saying.)
Lo que más me gusta es la playa. (What I like most is the beach.)
Trap: never use qué (with accent) here — question word ≠ connector. No entiendo lo que dices.
Cuyo/cuya/cuyos/cuyas = whose. It agrees with the thing POSSESSED, not the possessor.
El escritor cuya novela ganó el premio... (The writer whose novel won the prize... — cuya agrees with novela.)
Una ciudad cuyos parques son famosos... (A city whose parks are famous...)
In speech people often rephrase, but cuyo earns marks in writing. Remember: agreement follows what comes AFTER cuyo.
Traps for English speakers
These are the errors English speakers make most often.