what are the rules of the road when it comes to parking on curbs?

I took this pre-test online for the written driving test (esampletest.com) and i just don't understand the difference of uphill, downhill and level parking.. and which way to park the tires on these different levels. It's really confusing to me, I don't know why. Like why is it that you have to turn your tires away from the street(right)and ONLY uphill?.. so what if it has no curb.. and what if it is downhill.. and what if the downhill has no curb.. and like what is the point of the turned tires in a "SPECIFIC" direction anyway?... it says.. "left.. right .. 18" from the curb!... " but they don't explain why.. please help me understand... so that i'm not sooo confused :( my very first written driving test is on Tuesday Oct 12.. :) .. i really hope to pass! . i'm studying very very hard... oh and any other information on the rules of the road that you think are complicated to understand... Plzzz let me know.. thankks.. :)

Scott Stevenson	If the car slips out of gear, and the parking brake doesn't hold the car, you want to avoid having the car roll out into the street. Let's separate uphill and downhill, and it might make more sense. If you're parking uphill, and there is a curb, turning the wheel away from the curb means that the car will start to roll backwards, the front end will swing to the right, and the right front tire will bump up against the curb and stop the car. But that won't work if there is no curb-the car will just back out into traffic, because there is no curb to stop it. In that case, you want to turn the wheel toward the side of the road, so the car will just roll off the road. Parking downhill, you want to always turn the wheels toward the curb, or the edge of the road if there is no curve. If the car starts to roll, the front end will swing right again. The tire will hit the curb, if there is one, and stop the car. If there's no curb, the car will just roll off the road. It helps if you can picture what the car would do if it started to roll.

UCANTCME	Uphill and Downhill Parking Parking Uphill: - Turn your signal on and pull to the curb onto the gutter line or about 6-8 inches from the curb - Place the vehicle's gear lever in neutral - Turn the wheels away from the curb one full turn - Release brake pressure and roll back until the front tire touches the curb - Place the vehicle's gear lever in park Pulling away from Uphill parking: - Place the vehicle's gear lever in drive - Signal in the direction your pulling away from the curb - Check your blind spot over your shoulder in the direction your pulling away from the curb - Release brake pressure and straighten your vehicle's wheels while gradually accelerating Parking Downhill: - Turn your signal on and pull to the curb onto the gutter line or about 6-8 inches from the curb - Place the vehicle's gear lever in neutral - Turn the wheels towards the curb one full turn - Release brake pressure and roll forward until the front tire touches the curb - Place the vehicle's gear lever in park Pulling away from Downhill parking: - Place the vehicle's gear lever in reverse - Release brake pressure and if necessary tap the gas pedal to back 6-8 inches off the curb - Straighten the vehicle's front wheels - Place the vehicle's gear lever in drive - Signal in the direction your pulling away from the curb - Check your blind spot over your shoulder in the direction your pulling away from the curb - Turn the steering wheel 1/4 turn in the direction your pulling away from the curb - Release brake pressure and straighten your vehicle's wheels while gradually accelerating