Ο υπάλληλος στην τράπεζα μου δίνει έναν φάκελο και μου λέει να τον κρατήσω ασφαλή.

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Breakdown of Ο υπάλληλος στην τράπεζα μου δίνει έναν φάκελο και μου λέει να τον κρατήσω ασφαλή.

• να: to
• σε: at
• δίνω: to give

Questions & Answers about Ο υπάλληλος στην τράπεζα μου δίνει έναν φάκελο και μου λέει να τον κρατήσω ασφαλή.

Why does the sentence start with Ο υπάλληλος (definite article) instead of something like “an employee”?

Greek often uses the definite article (ο/η/το) when talking about a specific person in the situation/context, even if English might use a/an. Here Ο υπάλληλος points to “the (specific) employee” you’re dealing with at that moment.
If you wanted to sound more like “an employee (in general)”, you could say Ένας υπάλληλος…, but that changes the nuance.

What does στην τράπεζα consist of, and why is it written as one word?

στην is a contraction of σε + την (“in/at + the”).
So στην τράπεζα literally = “at the bank / in the bank.”
You’ll commonly see:

• στο = σε + το
• στη / στην = σε + τη(ν) The extra -ν is often kept before certain sounds and is very common in standard writing: στην τράπεζα.

Why is τράπεζα feminine, and how do I know?

η τράπεζα is feminine, so it takes feminine articles and forms:

• nominative: η τράπεζα
• accusative: την τράπεζα (which you see inside στην τράπεζα)
  Gender is a property of the noun and must mostly be learned with the article (e.g., memorize η τράπεζα, ο φάκελος, etc.).