You have already learned about relative pronouns and relative adverbs in previous modules. Both act as subordinating conjunctions when they connect sentences.
Relative pronouns, which include some interrogative and one demonstrative pronoun, introduce adjective or noun clauses. They are that, which, who, whom, and whose.
These are the students who have done well on the test.
These are the students. The students have done well on the test.
(Who replaces students when combining the sentences.)
Relative adverbs introduce adjective clauses: when, where, why. (Yes, that seems backwards, an adverb in an adjective clause.) They replace in which, which sounds more formal.
That is the museum where I saw the unicorn tapestry.
That is the museum in which I saw the unicorn tapestry.
Adjective clauses modify nouns. Sometimes in a sentence the noun modified by the adjective clause is omitted but understood.
Tell your teacher why you forgot your homework.
Tell your teacher (the reason) why you forgot your homework.
Other pronouns can introduce noun clauses. They are whoever, whomever, what, whatever, and whichever.
Whatever you want for breakfast is fine with me.
You want whatever for breakfast. Whatever is fine with me.
[Whoever ate the cookies] should have left them alone.
I expect [whomever I pick] to do a good job.