There’s many ways you can go about this. You could use divs for straight lines (not recommended). You could use JS to draw SVG lines (probably the best way) with something like Snap. Or, you could do it the easy to understand but time consuming way… which is draw an SVG in Illustrator or Inkscape, then reference the path via CSS/JS.
If you use ANY of these three options… ScrollMagic is the plugin that will make the lines grow upon scroll.
ScrollMagic has SEVERAL tutorials and excellent docs. You can figure out how to do pretty much anything with it.