I feel your heartache, I am all HTML and Dreamweaver too and it has taken me forever to get used to WordPress, but a lot of it is in understanding CSS, and a handful of PHP, but mostly CSS.
In answer to your question, just upload the entire folder to your wp-content/plugins directory. Don't worry about what's in it, just upload it. Then go to the Plugins menu in WordPress. You should now see the plugin listed amongst the others. Click "Activate", and you're good to go. Most plugins have optional features located in the Settings menu, you'll see the sub-menu down the bottom somewhere for the plugin you just activated.
Unless the plugin you downloaded is a widget for your sidebar, in which case you would find it in Appearance/Widgets in WordPress after the plugin has been activated. Drag the widget over to the sidebar and it'll appear on your blog. You'll probably find some customizable options within the widget.
The key to WordPress for me has been trial and error. Lot's of tweaking CSS and messing around with plugins and widgets, and TONS of clicking my browser's reload button. It is a slow process, but I think it's worth it, and it'll get easier with time. Altering the appearance of your blog is primarily done through all the CSS in style.css so if you don't know much CSS then you should read up on it because then fiddling with WordPress will be a little easier and make more sense. Good luck, and don't give up!