Ok a structure is a collection or group of Wiki pages, held together in a tree. Ok I guess an example is in order, imagine your writing some user docs and your going to use the Wiki to write these docs in. Ideally you would create a structure based on the name of these docs:
- System Requirements
- Apple Macintosh
UserDocs is the name of our structure
Introduction, System Requirements and Installation are like Chapters
and the others are link subchapters. That layout is called the "Tree"
so to sum up a structure is a way of organising your wiki pages into some form of controlled order.
At the moment you can only set permissions on each individual wiki page. But this isnt a big deal once you have the original layout defined. I use these wiki structures a lot on http://www.damosoft.co.uk for my customer user docs
The Wiki concept, well. thats easy to sum up as like a open or permission controlled web document, that anyone with the write permissions can edit without needing to know any HTML or have any HTML skills. I'm such if you google on wiki concept you will get a better description
You can always post back with what you find or if you want to probe deeper