As you move from simple to complex sentences in German, two structures become essential: Relativsätze (relative clauses) and subordinate clauses introduced by Konjunktionen. A relative clause gives extra information about a noun and always begins with a relative pronoun. The pronoun agrees with the noun it describes in gender and number, but takes its case from its function inside the relative clause itself. In the nominative, the forms are der, die, das, die (masculine, feminine, neuter, plural); in the accusative they become den, die, das, die; and in the dative they shift to dem, der, dem, denen. Two rules are crucial: the conjugated verb always moves to the end of the relative clause, and the entire relative clause is set off by commas from the main clause, as in Die Stadt, in der ich wohne, ist sehr schön.
A large family of subordinating conjunctions (Nebensatzkonjunktionen) also sends the verb to the end of the clause. The conjunction weil introduces a reason ("because"), while obwohl introduces a concession ("although"). For time relations, German distinguishes carefully between wenn ("when/whenever", used for present, future, and repeated past events) and als ("when", used for a single past event). The conjunction nachdem ("after") shifts the tense one step further back: a Plusquamperfekt in the nachdem-clause pairs naturally with a Präteritum in the main clause. Bevor ("before") and während ("while/during") complete the basic temporal connectors, and seitdem ("since") handles point-in-time references.
Another important conjunction is damit, which expresses purpose and is used when the subject of the main clause differs from the subject of the subordinate clause, as in Ich spreche langsam, damit du mich verstehst. When both clauses share the same subject, German prefers the infinitive construction um ... zu instead, but that structure is covered in detail in a later chapter. Mastering these conjunctions allows you to express cause, contrast, time, and purpose fluently, and it forms the backbone of coherent argumentation and narration in B1-level writing and speaking.