I think what you are noticing is just the movement of things. That is, animations and transitions.
To be honest, a few of those techniques couldn't be simpler. For example if you want a piece of text to slightly slide in from the left as the user scrolls down, that's just a wee bit of CSS.
Having a video background is also nothing fancy as long as the video is very well rendered and small in size. Laying it out involves some sizing techniques and layering elements on top of each other. Some tricks about that.
This technique is not possible without JS because under normal circumstances, images will either scroll exactly at the speed of the user scrolling, or maybe they are in fixed position and don't scroll at all. But they can't scroll at an alternate speed without help.
You might notice that once you've scrolled down and seen all these animations the first time (text sliding in, etc), you can scroll up and down and won't see them again. Once the text slides in, it's done. You'd have to refresh the page to see it again.
In any case, it is heavy JS, and heavy with images and videos. Of course it looks nice, has a "wow" factor, but is otherwise completely fluff and doesn't help people find the content they need. In fact many people would be thrown off and annoyed by so many pieces of the interface flying around every which way, it's really distracting actually.
That's not to say I don't appreciate a fine piece of animation here and there. I don't mind slightly shifting/sliding bits of text or images where appropriate. But the sight shouldn't break completely with JS turned off.
Just remember, progressive enhancement. Start with good solid content, then build up the fun stuff on top, don't make the site depend on the fun stuff or else fall apart.
If you want to know how to accomplish those "100% width" sites, there is nothing to it. Just don't set widths on things! Block level elements already stretch 100% wide. Other elements you might have to work with. Making images and videos stretch to such large widths is a matter of setting values for width, height, overflow, object-fit, background-size, min-height, min-width, and maybe some others. Vertically aligning/centering is still a frustrating task though.
If you want it to be responsive, then look for responsive grid systems to play with. The two biggest are Zurb Foundation and Bootstrap. These CSS grid systems let you decide how wide blocks are that align in rows and columns. For example at small screens you might want something full width, but on medium/large screens you might want it to be 50%/50% with some other content. Grid systems let you do this pretty easy.
Your homework (Googling):
1) Parallax effect.
2) Scroll detection, scroll effects.
3) CSS animations, transforms, keyframes, translations
4) Responsive CSS grid (Foundation, Bootstrap).
5) Full size background images/videos.
6) Hover effects.
7) Lazy loading.
8) Mobile-first design philosophy.
9) Progressive enhancement.
10) Since you use jQuery, I believe you can find plugins for all kinds of animations and scroll effects.