So why not go to Wikipedia and get this information? Why not research each on individually? You will never get multiple sources agreeing on what the 5 layers are. Heck we can barely agree on what RAM truly means.
Plus this is not a common term. 5 layers is not something used by IT or anyone else in the field. What you described is basically how a OS works. From the kernel to the GUI. It can be 5 layers or you can extend it to more.
As for the single user vs. multi user, what do you have to investigate? Simple answer. Single User only has 1 User. Multi Users does not. Both can be secure or insecure depending on if you do it right.
Cant help when the question is so vague. Plus we will only help guide you to answers. We will NOT flat out give them to you. This is for school and as such School is for learning. Getting the answer handed to you does not help you learn. It even states as much in our rules.