Setting image focal points ensures that the focus of the image is visible when the image is automatically cropped by Craft to fit into page content.
After uploading an image to an image field double click the thumbnail and then hover over the image to click edit.
In the modal pop-up screen find the focal point button and click that. Once you've clicked it you will see a black and white dot appear in the center of the image. Drag that image to where you want the focus to be.
Now save the focus point and when you also save the entry, the automatic transforms will ensure your focus point is in view.