This is the 2474th most frequent Spanish word.
acercarse
To approach or come closer.
In this sentence, 'acercarse' is used to describe physically getting closer to an object, the window.
María se acercó a la ventana para ver mejor el paisaje.
María approached the window to better see the scenery.
Here, 'acercarse' implies the act of going to or visiting a location, explicitly the store.
Cuando salgas de casa, acércate a la tienda y cómprame pan.
When you leave the house, stop by the store and buy me bread.
This use of 'acercarse' describes the teacher physically moving closer to the students to interact or communicate with them.