This is the 2834th most frequent German word.
strengen
"Strengen" means "to strain" or "exert" in English.
Here, 'strengen' is used reflexively as 'sich anstrengen', meaning 'to make an effort' or 'to exert oneself'.
Ich strenge mich an, die Aufgabe rechtzeitig zu erledigen.
I am putting effort into completing the task on time.
In this sentence, 'anstrengen' is used reflexively again as 'sich anstrengen', emphasizing the action of making an effort or trying diligently.
Der Lehrer verlangt, dass wir uns beim Lernen mehr anstrengen.
The teacher demands that we apply ourselves more in our studies.
Here, 'strengen' is part of 'streng', which is an adjective meaning 'strict', indicating rules that are firmly enforced.