Hello Sitepoint. I am a new user here, trying to find my way around the forum. I feel this is the best forum for web design and development and hope to get the assistance I need and contribute to it as well.

I have a question that is probably very simple:

So I know javascript, html and css (the basics). Thats great for basic we design. Im trying to learn how to create web applications similar to this:



Things that are "live" as I call the. Containing drag and drop features. A mobile website builder, similar to the one above, is what im trying to start with. Now I dont know which direction to go in, what langauge to learn, if it can be built with what I already know etc. and was hoping somebody could help me (tutorials, guides, advice, suggestions, etc.)

P.S.
Not to be offensive, but Im trying to build premium/professional web applications and would like information that will take me in that direction. Thanks in advance!