The Style editor appears when you choose New style or Change style. Because it includes too many options to put on the screen at once, it is split into several sections which contain items which can be considered together. (Historical note: this design precedes the introduction of tabbed dialogs in Windows!)
These options are listed on the left of the dialogue box. Click the radio button to display the section of dialogue box associated with it.
A small indicator box can be seen adjacent to each radio button. This will be illuminated green for any sections of the dialogue box which include options that have been explicitly set. This helps you find your way around the dialogue box, so that you don't waste time looking at irrelevant options when you edit a style.
Many options within the style editor, such as Bold, have two buttons associated with them. The first button decides whether or not the style affects that aspect of any text it is applied to. So, if you wanted to create a style which made text and numbers bold, you would make sure that the bold option was switched on, as in this screen. This means that when the style is applied to text or numbers, it changes the setting of that style attribute.
The second button decides what change to make. In a style which makes text bold, the second button is switched on as well, making it look as though it was pressed in, to change all text to which the style is applied to bold. If the second button were turned off, the style would have the reverse effect; it would look at all text it was applied to and turn any bold text it found to plain text.