The first part is indeed a bit tricky.
Push the boulder from the conveyor-button left on the conveyor, and immediately step off that button, so the boulder rolls over the red button.
Wait until a boulder is sitting on the red button, then stand on the conveyor-button again, until the rolling boulder is at the left side. Then step off the button.
Wait until the other boulder is sitting on the blue button, then quickly go left through the blue and red gate, and push a steelbox on the conveyor-button. Then get the other 3 steelboxes.
Let the first box stay on the button, and push a second box on the conveyor, which will destroy the rolling boulder. Then follow and push the boulders off the red and blue buttons, so they also will be destroyed. Collect the bonuscoins, and push the box on the other conveyor-button. A 3rd box should go on the pink button.
The rest should be not very hard, although not everything is visible. I hope this helps. If you need more, just ask.
