The Imagick class has the ability to hold and operate on multiple images simultaneously. This is achieved through an internal stack. There is always an internal pointer that points at the current image. Some functions operate on all images in the Imagick class, but most operate only on the current image in the internal stack. As a convention, method names can contain the word Image to denote they affect only the current image in the stack.
Because there are so many methods, here is a handy list of methods, somewhat reduced to their general purpose: