This is the 13375th most frequent Polish word.
otwieraj
"Otwieraj" means "open" (imperative form, used to instruct someone to open something).
Here, 'otwieraj' is an imperative in the second person singular, used to direct someone to perform the act of opening the door.
Otwieraj drzwi, proszę.
Open the door, please.
In this case, 'otwieraj' is part of a negative imperative, instructing someone not to open the window.
Nie otwieraj okna, jest zimno.
Don't open the window, it's cold.
Here, the verb is formed in a continuous aspect implying repeated actions of opening and closing.