This is the 1892nd most frequent Russian word.
поняли
"Поняли" means "understood" in English.
Here, 'поняли' is used in the interrogative form to ask if the listener comprehended the speaker's statement.
Вы поняли, что я хотел сказать?
Did you understand what I wanted to say?
In this sentence, 'поняли' indicates that the students grasped and comprehended the lesson topic.
После долгих объяснений студенты наконец поняли урок.
After long explanations, the students finally understood the lesson.
The word 'поняли' here is used in a declarative manner to express comprehension of the provided warning.