A family of Microsoft word processing software products for creating web, email, and print documents.
When you choose a new style set, what happens is that your style set will populate the Style gallery on the Home tab, making the new set of styles available to your document.
The new style set affects the formatting of styles in the following ways: If styles with the same names already exist in the document, those styles will be overwritten; if the styles do not exist, the styles in the set will be added.
Nothing will happen to text in the document, unless text paragraphs are already formatted in those styles. If none of the new style styles existed in the document, you will have to apply at least one of them to see any changes. There is an exception: if a style which is the based-on style for other styles (typically this means the Normal style) is part of the style set, you may see some "automatic" changes to existing text as a result of style inheritance.