Keynote is the Apple version of Powerpoint, another slide presentation program. It allows more in depth editing of slides, with easy transfer between it and other Apple programs. If a powerpoint was made in PowerPoint, Keynote can still open it, but make sure the Keynote presentation is saved as a .ppt, or PowerPoint won’t be able to open it.
Pages is a word processor, the same type of program as Word. It allows you to select from a wide variety of templates, which allows it to recreate the functions of Publisher, too.