A Relative Pronoun is a pronoun that introduces two types of clauses, namely, a relative clause/ adjective clause and a noun clause. The commonly used Relative Pronouns are which, that, who, whose, and whom.
“That,” “which,” and “who” are the Relative Pronouns that function as the subjects of the relative clauses.
When the antecedent is a person, the relative pronoun used as subject is “who”. The relative pronoun “which” is used when the antecedent is a thing. The relative pronoun, “that”, is used for both person and thing.
A relative clause is a clause that allows us to add more information or detail about a noun or pronoun. We can insert a relative clause into a main clause and behind whichever noun we wish to add more information about.
Example:
The man whom I work for is very nice.
In the above example, “The man is very nice” is the main clause. I wish to add the detail that I work for him, so I add the relative clause “whom I work for” directly behind the noun.
In German, we can add relative clauses the exact same way, but we have to keep word order in mind. Relative clauses are considered subordinate clauses, which means that in German, the conjugated verb is “kicked” to the end of the clause.
1. Relative pronouns
Most commonly, we use the definite article as a relative pronoun. The declension of a relative pronoun is slightly different from that of the definite articles.

Examples:
Der Schüler, den ich jede Woche unterrichte, macht große Fortschritte.
The student whom I teach every week is making great progress.
In the above example, the main clause is “Der Schüler macht große Fortschritte” (The student is making great progress). I would like to add more detail to the student, but I have to pay attention to the gender and case of the student in the relative clause. The sentence “Ich unterrichte den Schüler” (I teach the student) shows that the student has to be in the accusative case, so I need to use “den” as the relative pronoun, and the verb “unterrichte” is moved to the end of the relative clause.
2. “Wer” and “was” as relative pronouns
It is possible to use “wer” (who), “was” (what) and “wo” (where) in place of a relative pronoun. “was” is used only for non-living things, mainly after demonstrative and indefinite pronouns (das, alles, nichts, etwas), after nominalized superlatives (das Beste, was …), and to refer back to an entire clause.
“wer” is only used for non-specific people, and is typically used as an alternative to sentences with indefinite pronouns such as “jeder” (everyone), “jemand” (someone), etc., and demonstrative pronouns.

Examples with “was“:
Alles, was ich gegessen habe, hat gut geschmeckt. (non-living, indef. pronoun “alles”)
Everything (that) I ate tasted good.
Nichts, was du mir erzählt hast, glaube ich dir. (non-living, indef. pronoun “nichts”)
I believe nothing that you have told me.
Bestell dir das, was du willst. (non-living, demonstr. pronoun “das”)
Order what you want.
Examples with “wer“:
Derjenige, der ein Stück Kuchen will, soll sich melden. (pers., dem. pron. “derjenige”)
The person who wants a piece of cake should make themselves known.
This sentence can also be rephrased using “wer” as a relative pronoun:
Wer ein Stück Kuchen will, soll sich melden.
Who(ever) wants a piece of cake should make themselves known.
3. “Wo” as a relative pronoun
“Wo” can be used to refer to a place or space, a period of time, or an entire process. “Wo” as a relative pronoun could be translated with “in which”. It can also be substituted with “in dem/der/dem/denen” (dative: masculine/feminine/neuter/plural).
Examples:
In der Stadt, wo mein Großvater gelebt hat, gibt es viele Museen.
, in der mein Großvater….
In the city in which my grandfather lived, there are many museums.
In der Zeit, wo ich studierte, jobbte ich in einem kleinen Café. (colloquial; standard: in der / als ich studierte)
, in der ich….
During the time in which I studied, I worked part-time at a little café.
