If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
You need to get to the end of the track in the quickest time possible. Find the best way to navigate some of the what look like impossible boulders to get over. The foreground though covers some of the smaller boulders so you will have to edge forward carefully so that you do not flip your truck over and wreck the level.
Use the up arrow to accelerate and the down to reverse. The left and right arrow keys alter the way you can climb or go down.