El barco atracó lentamente al atardecer.

The ship docked slowly at sunset.

Breakdown of El barco atracó lentamente al atardecer.

• lentamente: slowly
• a: at
• el atardecer: the sunset
• atracar: to dock

Questions & Answers about El barco atracó lentamente al atardecer.

What does atracó mean in this sentence, and does atracar have other meanings?

Here atracó is the third-person singular preterite of atracar, meaning “to dock” (a ship).
Yes, atracar also means “to mug” or “hold up” (colloquial, for robbing someone). Context tells you which sense applies.

Why is atracó in the preterite tense? Could we use the imperfect (atracaba) instead?

The preterite (atracó) indicates a completed action: the ship finished docking.
The imperfect (atracaba) would suggest an ongoing or habitual action in the past—e.g. “The ship used to dock slowly…”—which changes the meaning.

Why is the adverb lentamente placed after the verb? Can it go elsewhere?

In Spanish, adverbs of manner like lentamente often follow the verb: atracó lentamente.
You could place it before or even split it:

• Lentamente, el barco atracó al atardecer.
• El barco lentamente atracó…
  But the most natural is after the verb. Word order can shift focus or rhythm, though.

What does al atardecer mean, and why not en el atardecer?