Structure of active directory

Hi,

So here is my problem.
I have just started as a network specialist in quite big company and I have on my responsibility our offices servers etc. The person who hold this position earlier hasn't document anything so I have quite massive work to figure everything out.

That's why I ask if there is some application or script which could give the active directory dependencies between groups,users etc.
That would be great help, so I don't need to do everything manually.

Thanks beforehand.