If you create your own custom styles or just want a quick way to view and modify existing ones, you should turn on the style area pane in Microsoft Word.
The option is tucked away: Go to File, Options, Advanced, and then scroll down to the Display section. Now enter a value in the text box next to Style area pane width in Draft and Outline views. Just enter "1 in" for starters; you can always make it larger or smaller later:
Now go to the View tab and click Draft to enable a view where this pane is visible. (You could use Outline, but Draft looks more like your final document – which is helpful when applying styles.)
You can double-click a style to open the Style dialog box, where you can quickly change between pre-set styles – say to No Spacing if you want to turn off default line skips between paragraphs:
Click the Modify button if you want to edit a style and apply the change to all content that uses it throughout the document:
There’s a lot of power in this feature, but if it ever gets in your way you can simply grab the vertical line that separates the style area from your content and drag it left to make it go away.