Learn Hardcore German: Beim Umsteigen stellte ich mein Gepäck kurz auf den Bahnsteig und lief dann schnell los. - While transferring I briefly placed my luggage on the platform and then ran off quickly.

Beim is the contraction of bei dem. Bei is a preposition meaning “at” or “during,” and dem is the dative article for the neuter noun Umsteigen. So beim Umsteigen literally means “during the changing (of trains)” or simply “while changing trains.”

Why is Umsteigen capitalized, and what part of speech is it here?

Umsteigen is a nominalized verb (a gerund), functioning as a noun in German. All nominalized verbs are capitalized and take an article (here implied in bei dem). It corresponds to “the act of changing trains.”

Could I say während des Umsteigens instead of beim Umsteigen, and what’s the difference?

Yes. Während des Umsteigens also means “during the train change.” However, während requires the genitive (des Umsteigens) and is a bit more formal. Beim Umsteigen (with dative) is very common and idiomatic in everyday speech.

Why is the verb stellte placed before ich in Beim Umsteigen stellte ich mein Gepäck…?

German main clauses follow the V2 rule (verb in second position). The first position here is the adverbial phrase Beim Umsteigen, so the finite verb stellte must come second, followed by the subject ich.

Why is it stellte and not legte or setzte?

Stellen means “to place something upright.” Legen would mean “to lay something flat,” and setzen is “to seat” or “to set someone/something down in a sitting position.” For luggage you typically use stellen because suitcases usually stand upright.

Why does the sentence use auf den Bahnsteig (accusative) rather than auf dem Bahnsteig (dative)?

Auf is a two-way (Wechsel-) preposition. When motion or direction is involved (“placing onto”), it takes the accusative case (auf den Bahnsteig). If it were describing location without movement (“standing on the platform”), it would take the dative (auf dem Bahnsteig).

Why is it mein Gepäck and not meine Gepäck?

Gepäck is a neuter mass noun (das Gepäck). The correct possessive pronoun for neuter singular in nominative/accusative is mein, not meine.

What function does kurz serve in stellte ich mein Gepäck kurz auf den Bahnsteig?

Here kurz is an adverb meaning “briefly” or “for a short time.” It describes how long the luggage remained on the platform.

Why does the sentence say lief … los instead of something like lieflos?

Loslaufen is a separable verb meaning “to set off” or “to start running.” In the simple past, the prefix los detaches and moves to the end of the clause: the root lief (past of laufen) appears in second position, and los goes to the end.

What role do dann and schnell play in und lief dann schnell los?

Dann is a temporal adverb meaning “then,” indicating sequence. Schnell is an adverb meaning “quickly,” describing the manner of starting off. Together they mean “and then set off quickly.”