Question formation in English involves (in most cases) the rule of Subject-Auxiliary Inversion (the subject goes after the auxiliary). If there is no auxiliary involved, as in the present and past simple, the auxiliary "do" is brought in. I find it helpful to mention to students that "do" can also be used in affirmative sentences, though this usage is rather marked in modern English: for example "it does mean" is an alternative to "it means" (only different in emphasis).
In modern English, only auxiliaries (and the copula) undergo this form of inversion. (I include modals as auxiliaries.) This is in contrast to French, and also older forms of English ("where goest thou?").
Afterthought: since you are living in Germany, it is easy for Germans to confuse English interrogative word order (Subj-Aux inversion, as described) with their own rule that the finite verb must come second, which also involves the postposition of the Subject in questions, but is of course not the same rule.
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