Draw the ramps. Drop the marble. Try to get it into the bucket.
Any of these can be edited — rub bits out, draw over them, add a peg where it needs one.
Draw a ramp under the funnel, then drop a marble on it.
The marbles are not following your ramps — they are bouncing off them. Each one is a circle with mass, spin and a bit of bounce, rolling under gravity; each ramp is a solid bar standing exactly where you drew it. Nothing is on rails, so a marble can hop a ramp, ride the wrong side of it, or sit in a corner and refuse to move, all of which a real one does too.
A shallow ramp keeps the marble; a steep one lets it build up speed and jump. Pegs are for slowing it down and for sending it somewhere you did not intend. Every drop leaves a faint trail behind, so you can see where the last one actually went rather than where you thought it went.
Whatever you build stays in this browser until you clear it.