I know it's kind of an 'open' question to ask but I simply don't know where to start. Let me first tell you a bit of my experience/background so you know the level I'm at:
I can share my experience with Cordova.
I work like full-stack developer and i'm quite expert to build responsive website, so the natural step to approach mobile dev was try Cordova.
First You can start to build HTML document totally responsive and try as webpage on your target devices. A cool stuff, targeting mobile devices, is that You can use new CSS3 directive, without worry for compatibility with old browser.
First I installed Cordova following this tutorial. https://ccoenraets.github.io/cordova-tutorial/create-cordova-project.html Opening the folder /www on your project you can edit your app like a website, and you can also debug with the browser like a normal site.
To enhance the feature you will find a lot of plugins ready on github to extends the native functionality at the Cordova/phonegap project.
I suggest you also to build using onsen http://onsen.io/ a framework that let you use mobile UI easily.
Last tip that i can give you, if you target Android is try your apps on virtual machine, i use Genymotion https://www.genymotion.com/ that is much more fast then SD<
Good luck with your first app!