This is the 2127th most frequent Polish word.
ostrzega
"Warns."
In this sentence, 'ostrzega' is used in the present tense to indicate that someone is currently giving a warning or advice aimed at caution.
Ojciec ostrzega swoje dzieci przed niebezpieczeństwami.
Father warns his children about dangers.
Here, 'ostrzegł' as 'ostrzegał' is used in the past tense to indicate that someone gave a warning in the past.
Lekarz ostrzegał mnie przed konsekwencjami złej diety.
The doctor warned me about the consequences of a poor diet.
In this usage, 'ostrzega' is referring to a professional warning issued based on analysis or predictions.