A subordinate clause is simply a sentence embedded in another sentence. In Spanish, it's called an "oración subordinada" or "oración secundaria", literally a "subordinated sentence" or "secondary sentence".
The 'sentence-in-a-sentence' can act as an adjective, an adverb, or a noun.
as an adjective - which one?
an adjective describing which lady
· That FUNNY lady is my Spanish teacher.
· That lady WHO IS WEARING A SOMBRERO is my Spanish teacher.
as an adverb - when? where? how? how much?
an adverb describing when he runs
· He runs NOW.
· He runs WHEN HE HAS ENOUGH TIME.
an adverb describing where he runs
· He runs HERE.
· He runs WHERE THE PATH IS PAVED.
an adverb describing how he runs
· He runs QUICKLY.
· He runs HOW HIS COACH INSTRUCTED HIM.
an adverb describing how much he runs
· He runs A LOT.
· He runs AS MUCH AS HIS DAD RUNS.
as a noun - what?
a noun as subject of verb
· SOMETHING is foolish.
· THAT HE ISN'T WEARING A COAT is foolish.
· SOMETHING impresses us.
· THAT SHE SPEAKS RUSSIAN SO WELL impresses us.
Note that, in English, if the embedded sentence is the subject, we usually move it to the end, and we have to insert a 'filler' subject in front:
· (IT) is foolish THAT HE ISN'T WEARING A COAT.
· (IT) impresses us THAT SHE SPEAKS RUSSIAN SO WELL.
a noun as object of verb
· The teacher asks SOMETHING.
· The teacher asks THAT WE SIT QUIETLY AND LISTEN.