This is the 3495th most frequent Spanish word.
fijar
To fix, set, or establish.
In this instance, 'fijar' refers to concentrating an abstract concept like attention on a specific subject.
Intenta fijar tu atención en lo que estoy explicando.
Try to focus your attention on what I am explaining.
In this sentence, 'fijar' is used in the sense of deciding and establishing a specific time for an event.
Voy a fijar la hora de la reunión para mañana.
I will set the time for the meeting for tomorrow.
Here, 'fijar' implies attaching or securing an object to a surface, ensuring it stays in place.