This is one of the most common questions that comes up during the initial assembly. First you will need to remove the plastic part that protects the hub of your front wheel. It is not a part of the bike and is there for transportation purposes only.
It is not always easy to remove it and the outer part may break off, leaving a piece of plastic in the axle. If this happens simply take the quick release skewer and push it out from the other side.
Once again, the plastic cover is not a part of the bike so don't be afraid to break it.
Loosen and remove the nut at the end of the quick release. There is a cone-shaped spring that will come loose with the nut. Do not lose the spring.
Slide the quick release through the side opposite the disc brake disc.
Slide the tapered end of the cone-shaped spring onto the left side tip of the quick release.
Screw the nut onto the left side tip of the quick release. Do not tighten the nut fully.
Swing the lever on the left side of the quick release to the "close" position. The lever should offer moderate resistance when closing. If it does not, tighten the nut further. If the lever cannot be closed because of too much resistance, loosen the nut.
This video does a good job of thoroughly explaining and illustrating the adjustment process. It is about 3:30 in length: