Hey there. What you're talking about is basically informaton system design and yes, there are whole BA and masters' degrees dedicated to that. So before you rush into this idea, mortgage out your house, and quit your job saying 'see ya, b*tches, I'm gonna make my own learning platform with booze and hookers', I'd recommend take a step back and breathe :))
Ok, joking aside. I took the Responsive Web Development coursera specialization and they go over the basics of html, css, and then focus on MeteorJS. In my humble opinion, depending on your usecase, you could create your whole platform in MeteorJS (I mean, could you create your own Lynda in Meteor? Nope. Could you create your platform for like couple hundred concurrent people at the peak time? I think absolutely yea).
The side effect is that you'll:
a) Start out your html, css, and JS journey
b) Do both server-side and client-side programming
c) Get results fast (meteorJS is basically a prototyping platform as far as I understand it)
d) Get some idea of how stuff works.
When you finish all the courses in the specialization, which can be done for free if you don't care about the cert, you can think about what's next. Check in here for some more advice if you require more pointers.
That would be just my humble advice. Hope this helps!