This is the 3227th most frequent Polish word.
spokojnie
Calmly; peacefully; take it easy.
Here, 'spokojnie' describes the manner of resting, meaning to do so in a peaceful or quiet way.
Chciałbym spokojnie odpocząć po pracy.
I would like to rest peacefully after work.
In this usage, 'spokojnie' indicates the relaxed and composed manner of his actions.
Spokojnie poszedł do drzwi, aby je otworzyć.
He calmly walked to the door to open it.
In this sentence, 'spokojnie' is used as an adverb to reassure someone, similar to saying 'calmly' or 'relax' in English.