I've been a C++ programmer for 3 years now. Dabbled in C#/Unity and Python and recently I was tinkering with an API using C++, cURL and Jsoncpp. One of the apps I've made using said API is pretty good, but it has no place as an executable - why would you use an executable you have to download when you can do the same operation on a website?
My knowledge of web development/web app development general is extremely limited. I know a little bit of HTML/CSS and practically nothing else. I've heard of terms such as GET, POST etc but only have a super vague idea of where to start. I'd like some advice on where I should begin if I want to create an app on a website. Would HTML/JS do the job? Do I need to look into PHP? MySQL won't be needed as the API returns all data in Json.
TL;DR Wanting to start developing basic apps to plop on a website, any good resources/tutorials/advice for this?
EDIT: I'm aware this isn't strictly game related, but the API is for a game if that helps! The app I'm thinking of is interactive either way and I've been on these boards for a fair while - probably the best place to ask.