The x and y parameters specificy where, (in this hypothetical scenario), you would place the cursor. 0,0 often makes sense, but for this example lets imagine you use to x:20, y:20.
You also pass (the address of, &) x1 and y1. After getTextBounds() has run, x1 and y1 will have been set to the location of the top-left corner of the text.
For the default font: this is the same as x and y (20, 20)
For custom fonts: the text is often not drawn from the top-left corner. setCursor() often specifies where the first character would sit, if you were to handwrite it on a piece of ruled paper.
Most of the text will likely be above the cursor; a small part may be left of the cursor. getTextBounds() with x=20 y=20 could give you values like x1=18 y1=10.