1)sets of paralel lines IRL meet in a “vanishing point” on the drawing somewhere
2)if such sets are horizontal IRL, on the paper they meet on the horizon line. It is a custom to draw vertical paralel lines - just as vertical, but propperly, they ought to have a vanishing point on the vertical line that cuts the horizon in the eye-projection on the paper. useful: skyscrapers, frog-perspective etc.
3)if you're for real, measuring is everything. when you're imagining and drawing things, just make it believable enough.
Cheers!!