Unless you are intending on using Dreamweaver to manage a WordPress site then you may have the wrong idea about how WordPress works.
Think of Wordpress like the a modifiable car. You start with a basic model, off the shelf components. Nothing wrong with that it will do everything you need to get from A to B. Self contained it doesn't need anything (like DW) to work. However with a little love or some specific requirements you can take that basic car and modify it so it looks awesome, or it goes faster, or it drifts well, or it can race in a rally, or drag race.
The plugins that you add are like upgrade components. They might tweak what is already there or they may replace it, or add something new.
Themes are like the paint job, but some themes come with optional extras (bonus plugins cause the theme maker likes you).
You can use Dreamweaver to help manage a WP install but personally I've never done it, I haven't needed to. Wordpress is modular so it is easy to add plugins and themes, you install them from the WordPress admin, then turn them on. That's it. Some require a setting or two to be changed but at the back end those new features are available as soon as you activate the plugin.
Most themes are also modifiable. So you install them, then create a child version (essentially just a custom folder that allows you to overwrite the themes defaults without changing the CSS or php files directly) and you can modify the CSS or add your own functions easily. If the theme gets updated, you can update knowing that none of your customisations will be lost.
Hope that helps a little. It is a different way of working than a straight HTML/CSS. My workflow has been one of trying to use or get as close to a final product using WordPress tools, then tweaking the CSS to make the website unique or tweak the areas that don't quite work. This is easily possible with WP and not a lot of work.