Import your image onto the Canvas – File – > Place
Scale the image smaller or larger until you are happy (use the shift key to scale in proportion)
Rasterize the image (right click on it’s layer and click Rasterize layer)
Draw your shape layer above it – could be a rectangle for a banner area or a circle for a button.
Select the vector mask of the shape layer you have just drawn above the image
To do this – Hold the CTRL key and click on the vector mask of the layer.
Click back on your image layer and press CTRL + X, this will cut the portion you want from the image.
Press CTRL + V to paste this portion onto a new layer.