In that case, you need to do a Local Install. But that means you then have to upload the changed pages and still upload any images via FTP which is more complicated. You can make most changes within WP Dashboard -- which is set up to need no knowledge of coding. There is a visual editor built in, although you can also view the html code.
IF you do end up wanting to modify code itself, you do not need Dreamweaver -- but just a basic text editor.
What you might want to do just to familiarize yourself with how WP works is to create a free "practice" site on wordpress.COM -- which is a fully hosted site that has the same basic functionality (though more limited) of wordpress.ORG sites. You won't have all the options -- unless you pay for them -- but you'll get an idea of the general set-up and how it works. Once you have a better idea, you'll be able to make a more informed decision about local host or not.