REWARDS - $10,000 (maximum; can be lower), Respect, Imports/Exports unlocks
Get in the car with Cesar and head for the docks, marked by a yellow blip. When you get there, go inside the red marker and press Triangle to enter the crane. Press the left analog stick to adjust the crane's position. X lowers the magnet while Square raises it. Press Select to change your view if you need to do so. Simply let the magnet hit the top of a crate to let it attach.
Once you have a crate, maneuver the crane over to the red marker on the dock. Once the shadow is over the marker, gently lower the magnet to the ground and press the Circle button to release the crate. If you drop the crate from too high, the crate might bust open and you could destroy the car inside, which will result in you failing the mission. No matter what crate you choose, the third one will always be the car you need.
When you drop the third crate, Cesar will drive the car out of it and some thugs will pull up and begin firing. Exit the crane and kill them, making sure that Cesar doesn't die. After you kill them, a second car pulls up with 3 more thugs. Kill them and then two guys will approach on foot. Once you kill them all, get in the car and head back to your garage to finish the mission. A maximum of $10000 can be earned, with money taken out for damages, and respect earned.