How does the mouse pointer change when you move it to the edge of a window? What happens when you left-click and drag the mouse pointer when it looks like this? Repeat this experiment with the mouse pointer at the corner of a window.

What will be an ideal response?

The mouse pointer changes to an arrow pointing to a line. When you drag
this arrow, you resize the window. When you position the pointer on an
edge of the window, you can resize the window in one direction. When you
position the pointer on a corner, you can resize in both directions at once.