Bible Maps in The Bible Study App work much like other enhanced resources. As you are reading in the main window, the resource guide will look at the maps you have installed and pull up relevant maps that you can easily access.
To zoom in on a PC simply hover over it in the resource guide and use your mouse wheel to zoom in or out.
For Mac you can use a trackpad or magic pad.
On mobile devices pinch to zoom.
Check out the video below that demonstrates the zoom feature on a PC running The Bible Study App.