After exiting the hospital and trapping zombies inside, Newbie sees a helicopter and tries to get it's attention. He follows the helicopter through the bridge.
It can be found on top of the first bus.
It's in the green dumptruck hanging on the edge of the bridge.
This is a bridge that has collapsed, with a medical tent and a giant mechanical gate in the back, behind where you spawn. The rest is an assortment of crashed buses, cars, and police cars. Some cars have the headlights on. There is a room with bloody bags in the tent, presumably containing bodies.
Do not get too close, as the monsters will hit you.
Kill the monsters as quickly as possible, since you earn a star by killing monsters quickly. Do not rush it, though.
Use pets, as a minor/major backup for killing.
Follow the green arrow that appears once there are 5 enemies left, in order to kill the enemies quicker.
Restore your ammunition by quitting the level and coming back. However, try not to do this when you are about to complete the level, as the amount of killed monsters will be wasted.
Use Armor. If you have a decent amount of armor, you will not have to worry about getting damaged, because you can get 3 stars even if you have damaged armor. This doesn't apply to Health.
The enemies aren't extremely tough in this level, so you can equip the weapons with a decent amount of damage.
However, almost all of the enemies appear at the end of the big part of the broken bridge, so it is best to pick them off from a decently long range.
Dodge the explosive wheels of the Infected Truck Driver.