It's good to have some basic knowledge about networking before starting to learn about WebRTC.
Basic knowledge about IP addresses & Ports (Sockets) and about P2P networks
should be enough. And yes, knowledge about JavaScript is important to code WebRTC based web applications and some knowledge about NodeJS or other server side languages if you want to implement a signalling server for the WebRTC application or you could just use some code in GitHub.
But it's fine, you can still learn WebRTC with some abstraction, it's just that you might get confused with what's going on
or might wanna know the subject in a more better manner to wrap your head around it.
Here are the resources, in order :
1.https://www.html5rocks.com/ is a great place to start with.
Try this page first : https://www.html5rocks.com/en/tutorials/webrtc/basics/
It's too big! So, to get a quick overview, check out the YouTube video embedded in the site. That itself is 40 mins long though!
2.You could see some WebRTC samples in action over here : https://webrtc.github.io/samples/
3.Now, with all the motivation you can try some code. Head to https://codelabs.developers.google.com/codelabs/webrtc-web and code a video chat web application on the go!
It's a bit outdated code, in terms of socket.io stuff.
4.While learning to code, you will get to know about adapter.js. It is a shim to insulate apps from spec changes and prefix differences. In fact, the standards and protocols used for WebRTC implementations are highly stable, and there are only a few prefixed names ( like webkit_xyz_, moz_xyz_ ). For full interop information, see https://webrtc.org/web-apis/interop.
5.Now that you know how to code in WebRTC, you would now understand that it's not very easy to code it. If you want some good WebRTC libraries to do the heavy lifting, so that you can code your Web app in a more polished manner and concentrate more on your App logic code than on WebRTC code, you could just use libraries like Simple-Peer, PeerJS, SimpleWebRTC. You can look out for some more by searching in npm or GitHub.
6.Some sites and YouTube channels to look at for fun WebRTC stuff :
https://www.youtube.com/user/FreeTheFeross/
https://www.krankygeek.com/
https://webrtchacks.com/
https://simplewebrtc.com/notsosimple.html
Official site to check about WebRTC : https://webrtc.org/ And they also have a Getting Started guide, most of the resources I mentioned are pretty much there and there's lot more to it, so check it out!