When you tell a friend what someone else said, you typically say something like "he said he's tired" or "he said he'll come," largely keeping the verb form close to what the original speaker used, just adjusting the pronoun. German has a more precise mechanism for reporting other people's words, called Indirekte Rede (indirect/reported speech), and it can call for a special verb form with no direct equivalent elsewhere: Konjunktiv I.
The basic idea is simple: instead of quoting someone word-for-word in quotation marks, as in direct speech — Er sagt: "Ich bin müde" — you fold it into a clause depending on a reporting verb like sagen, fragen, behaupten, or meinen. This merging happens in one of two ways: either with dass, where the verb moves to the end of the clause like any other subordinate clause, giving Er sagt, dass er müde sei; or without dass, where word order stays nearly normal but the verb form itself changes, giving Er sagt, er sei müde.
The most confusing part for learners is choosing the right verb form. In formal language, journalism, and writing, Konjunktiv I — forms like sei, habe, komme, könne — signals specifically that these are someone else's words, not a claim the speaker personally vouches for. In everyday spoken language, though, people often fall back on Konjunktiv II or even plain present tense, especially when the Konjunktiv I form is identical to the ordinary present and therefore not distinctive, as happens with most verbs in the ich and wir forms. This careful split between a formal and an informal register for reported speech is something many languages handle only with a word like "that," without any change to the verb's conjugation.
Reported questions follow a slightly different rule: if the original question was yes/no, use ob at the start of the subordinate clause — Er fragt, ob ich komme. If it used a question word like wann, warum, or wo, that same word stays and becomes the connector, with the verb moving to the end — Er fragt, wann ich komme.
The most common mistake is forgetting that the verb goes to the end of the subordinate clause after dass or a question word, writing Er fragt, wann komme ich instead of the correct Er fragt, wann ich komme.