Information about the job's tab

[Naturalfire0]

i'm not sure if its the braincells i've lost arguing with some people in game but i never noticed until just recently under the jobs tab in CA: classic there is entrustment jobs and when i look at them it seems straight forward except the random gun parts with the description but when i tried doing them i must not understand what exactly the game wants from me and i can't find any guides or info about what entrustment jobs are period if anyone can help me understand? it would be much appreciated.