For me to be productive, I need to understand the entire system without too much help. Other programers are really busy and dont' have time to hold my hands.
You should take this is a danger sign. You might want to look for greener pastures.
There should be a big picture presentation of the system as a whole. Multiple such big picture views. A cartoon for management, a more detailed one for the system architect, a different view for the system integrator. They should have shown you those pictures on day one and walked you through it. Someone should be mentoring you along, pointing you to training materials, tutorials, and documentation; showing you the online resources; checking on your progress; and be available now and then to answer questions you have. You shouldn't expect the mentor to spend all his/her time with you, but that mentor should be there.
With a large system it might take months, sometimes several months, for you to come up to speed and become a productive asset to the organization -- and that's with a proper system in place. Without a proper system in place, odds are good that nobody understands the system as a whole. The programmers are too busy because they're busy making a convoluted mess that will eventually come crashing down on them.