The difference between desktop publishing and mere word processing is in the layout. While modern word processors provide great capabilities in this area particularly in the realm of justification, columns, and tables, they still fall short of the pinpoint control and accuracy required for publishing. Because desktop publishing is primarily about the eventual printing or other creation of a physical document, the precise layout and color matching becomes as important as the content. If a user is to be able to be confident enough to order 10,000 copies of a publication, it is necessary for the user and the printer to know that there will not be any glitches or issues due to a difference in formatting caused by versions, or margin settings, or a different interpretation of "magenta". Such precisely laid out documents are known as "print ready" and they are the purpose of Scribus.
Scribus is primarily aimed at professionals which means the user interface can at times be unintuitive. However, there is usually good reason for such things. For example, inserting an image that is too large for the space allotted results in a cropped image not a resized one. While resizing is the way to go in standard word processing, there are few professional publications that would settle for the quality of image made by such embedded resizing and would instead insist on the image being resized at the highest level of quality prior to being used in the document. Thus, cropping makes more sense for a professional level product like Scribus.
Don't let the word professional scare you, though. Scribus comes with tons of easy to use features and templates including dragging and dropping elements, tools and wizards, and easy to use measurement features. Scribus also comes with its own Story Board so that you can do your text typing off layout.
That means that whether designing a professional newsletter, poster, manual, magazine, or book, Scribus can give you everything you need without costing you a dime.