As a web developer myself, i'd recommend first of all getting comfortable with HTML and CSS. Try designing and then building something just with the very basics.
Then start looking at frameworks. Something like twitter bootstrap can be used to do a lot of the heavy lifting of regularly used components. Try building a site with bootstrap to get familiar with it.
Then the next step is to integrate the site into a CMS, like Wordpress. This is the biggest learning curve, as Wordpress is simple, yet vast. There are millions of combinations of ways to manipulate it.
I'd recommend Sublime Text as a code editor. I use Coda myself, but Sublime Text is really similar, and free. Always build from scratch when possible. Taking a pre-built theme and stripping it back ends up with messy, bloated code. Start simple, and build features in as you go along.
I've been a web dev for 17 years now, and i'm still learning new stuff every day, so it won't just happen over night!