People are dependent on the supplies and sometimes the supplies can't be delivered since there is a shortage in the production. Most of the time, this has something to do with the fact that there is not enough for it. Other times, the production plant can't produce enough as it can't cater to the demand. Whatever the reason, the supply needs to be met and the only way to get enough of it is through getting it from other countries. After, it is delivered at the port, which is when the truck is needed. The truck driver then needs to deliver it to the construction company, wherein it would be use.
Of course, there is the quality check that needs to be done since you might not know if the materials are sub-standard. A sub-standard material would only endanger the construction of the new building. There are many process to check the quality of the material, but it has nothing to do with the truck driver. The truck's driver main concern is the safe delivery of the material since that is what he is paid for. If he lost some of the materials then his career would be endanger.
The idea of the game is to get to the parking area as fast as you can, but it doesn't necessary mean that you should forget about driving with care since that is a prerequisite for all drivers. Also, you might hit a man, which would instantly end the game. Once, you have done that, you failed that level and you need to do it all over again. Also, try not to hit other vehicles in the area as that would damage the truck too. If it takes too much damage then you would fail the game. The game becomes harder and much more difficult as you make some progress.