The Ionic framework is for developing cross compatible, responsive applications. It has a massive library that will give you all the functions you need to create stunning, responsive applications. You can also port these creations to IOS/Android (this is not a seamless process! And you’ll need advanced technical knowledge to get a good grip on the typical native functions).

There are some amazing tutorials on Udemy that can get you up and running with Ionic, but they will only get you so far. Angular is a useful skill to pick up on your way, it’s been improved constantly since its initial release. This will help you get the majority of code working how you want it to.
Personal experience
I’m on my second brush with Ionic, and it’s becoming a solid way to develop apps. It’s fast to get up and running, but full of quirks… be prepared to hit stack overflow a lot, digging for solutions to some very odd problems. It’s probably the closest thing to a unified development platform we’ll get though (yet).
Use cases
Need an app developed for IOS/Android, or a responsive web site that’s using up-to-date tech?
Cons
Like nearly every other code base (apart from Python), it can be a totally mystery why something isn’t working as you’d expect. I guess this happens with larger frameworks where many people are working in the same space… some things go terribly wrong. Oh, and be prepared to pay out 12k if you want Ionic to sort your code issues out for you!!!