To start with the simplest, relative clauses, also called "adjectival clauses", simply act like adjectives, and are also treated as such.

Lèn lûngyóng là yóng zâi qìgó gon
"The building that just burnt down earlier today sits in the middle of town."

Xèyân de líung wun fénkù nomtá
"My friend who used to know how to sing (and no longer knows how to)."

Subclauses equivalent to "Haci knows that Saba can't swim", or "Why Saba can't swim (that) is unknown", called "content clauses" or "noun clauses", where the subclause ("Saba can't swim") can be the subject or object.

Content clauses are constructed more-or-less the same way as in English (albeit without "that"); plus, they have to include fén if it is in the present.

Haxi mēlíung Saba hongqè líung tì pè
"Haci knows that Saba doesn't know how to swim."

The tense in the content clause tends to match the main clause, though sometimes they differ; adverbs clear up most confusion.

Xèyân fâule là ké sàng qú là
"I heard you speak just a second ago."

Cainye can also have the content clause as the subject; the actual content is treated as the possessor (or relative clause) of the equivalents to "whoever/whomever", "reason", etc.

Ké dekāte là de míun làngdi ngā!
"The reason you just did that is stupid!"
(lit.) "you just did 's reason is stupid"

Bāu róng siùt kù cánlùt de fón cém yéixèi pèlà
"The person who found the money two days ago must give it back."

Another type of subclause is an adverbial clause, Cainye attaches them to verbs with prepositions or adverbs, and de (beware of the verb de, which means "go somewhere"). These are like relative clauses for verb

Màng lò bùwèng kù Haxi de yéi kù
"He came back after (when) he saw Haci."

Xêyàn lò lèn de là Gugenheim de dóm de là xêyàn gīyóng
"After I went to the Gugenheim earlier today, I quickly went to my hotel.