Galleries allow for different image types and sizes to be grouped together. Each Gallery can have its own set of images sizes which are genereated whenever an image is uploaded into the gallery.
Below is instructions for setting up your own Gallery.
Getting to the Gallery Admin Popup
Adding a new Gallery
Gallery Sizes
Gallery Size examples - Only specify width
Gallery Size examples - Force width and height, padd with colour
Gallery Size examples - Force width and height, crop