I'm loosely following this tutorial: https://www.youtube.com/watch?v=zgZoWYYWzeE&list=PLiavqwl4YqPirG3qYsI-n95t55y05CUVJ [www.youtube.com]

I'd like to hide the lines until they collide with the grid. The ‘pop collision detect’ seems to output a Hit Num Attribute as shown in the screenshot but I have no idea how to use that data to hide the lines. Specifically I'd like to hide the points inside the line, I wouldn't want the whole line to pop in existence as soon as it touch the ground if possible (unless it makes things a lot more complex, then I'll be fine with this haha).

Thank you,
and obviously I'm very new to this.

You could try setting the @Alpha attribute based upon hitnum. It might not hide it in the viewport, but with the correct material, it should work for the render.

Otherwise, perhaps try carving the line based upon the hit count..?