Hope this is on topic but this has been driving me crazy for a couple of months now and I stillhavent got BISS working. People have been really helpful on here and I am learning as I go but one of my questions was what the ch mod actually does in terms of file permissions.

644 gives some access to the file. 755 gives greater access and 777 gives full access. Is it hierarchical like that or do the different values give subtly different properties to the file?