The Hand tool is designed to scroll the displayed area of the image in the window if the whole image doesn’t fit into the window at the chosen scale. To move the image you should press this button, put the cursor onto the image, press the left button and, keeping it pressed, move the image in the window.
Even if another tool is active, you can press the spacebar on the keyboard and drag the image with the left mouse button to scroll the image in the Image Window.
Use the buttons in the Tool Options panel above the Image Window to adjust the image scaling:
100% (Ctrl+1 on Win, ⌘+1 on Mac) - the image is displayed at its actual size;
Fit to View (Ctrl+0 on Win, ⌘+0 on Mac) - the image is fully visible in the Image Window;
Fill Window - the image is scaled to fill the Image Window completely.