I went your exact route -- started off thinking I might want to learn some coding stuff, started checking out online resources and found some books, went through them, went through a bunch of Lynda.com tutorials, did more tutorials, asked friends and acquaintances questions about what to learn and how to do things...
...I started off building a simple WordPress site for a side business I have teaching guitar. From there, I took on challenges to increase the functionality of the site and customize the design.
Then, I looked around for another test project and found an obvious one building another relatively simple WordPress site for a friend. Then I did another. And another.
Then, people started asking me about what I was doing and if I could build them a site.
One day, after finally getting the hint, I posted an ad for doing WordPress work on Craigslist and got a bunch of calls. I've been riding a nice wave of supplemental income ever since and have continued moving deeper into more interesting areas of coding. And I've gathered a nice stable of clients, gotten a bunch of great referrals, have a solid portfolio and it turns out I really enjoy the work, the flexibility and the challenge of working on websites.
So I say go for it, dive right in, start by building a site for yourself or someone you know who needs one. Research, read, study, ask questions and keep going -- and it absolutely can become a great side gig. At this point, I've actually let my other things grow smaller to make more room for the web dev stuff.
To reiterate what someone else said here, you'll also always be able to find work. I'm amazed at what a difference being in web development is in terms of demand -- it's very very very easy to find clients who are looking for someone just like you wherever you're at in your learning curve.