A named style is a set of appearance settings that has a name and can be shared by elements of the same type.
Be careful not to confuse this with model that makes everything the same - the content and appearance.

Styles can be modified from element popups.
To create a style, then from the "Style" dropdown list select "New ..." and save the new style with the chosen name. All current settings of the element are saved in the new style.
To apply a registered style to the selected item choose one of the applicable styles in the dropdown list.
To modify an existing style click "Edit selected style". When an element has a named style, this one is selected by default; to modify the local style, select stye "Local".