Nie mogę wejść do wagonu, bo drzwi się nie otwierają.

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Breakdown of Nie mogę wejść do wagonu, bo drzwi się nie otwierają.

• drzwi: the door
• nie: not
• bo: because

Questions & Answers about Nie mogę wejść do wagonu, bo drzwi się nie otwierają.

Why is mogę used here instead of umiem?

Because móc means can / be able to in the sense of possibility or circumstances, while umieć means to know how to or to have the skill to. In this sentence, the problem is not lack of skill; the problem is that the doors are not opening. So Nie mogę wejść... is correct.

Why is the infinitive wejść used instead of wchodzić?

Wejść is the perfective infinitive, and it suggests one completed action: to get in / to enter. That fits the idea here: the speaker wants to enter the carriage once. Wchodzić is imperfective and would sound more like to be going in, to go in repeatedly, or to be in the process of entering.

Why is it do wagonu?

Because do takes the genitive case in Polish. The noun wagon therefore changes to wagonu, which is the genitive singular form. So do wagonu means into the carriage or to the inside of the carriage.

Why not w wagonie instead of do wagonu?