As this is A Dummie's Guide I would like to add this very simple, introductory guide which Geraint posted in January 2009. I was very helpful to me at the time, and I have been back since, to refresh my memory.
"I found the following to be a simple way for schoolkids to grasp the situation, and for adults in evening classes. Relating the army set up to something they could immediately grasp. Room for corrections I know, but it worked for me.
Regiment is your secondary school.
Your 'year' is your battalion.
In that 'year' you are a member of a form class - your 'company'. In classes, you are split up into smaller teaching groups - your platoon/sections.
Your 'form teacher' is your Lieutenant. Your 'Head of Year' is your Captain, Your headteacher is your Lt Col officer commanding.
Your subject teachers are various NCO and Warrant Officer instructors.
Your canteen, cleaners, groundsmen and caretakers are the ASC and Labour Corps. Contractors working on the school are Pioneers and RE.
Your school and the three nearest to you are one Brigade. All the schools in Denbighshire are a Division, with the director of Education the Divisional Commander
In 1914, instead of one entry class coming into school in September - there were five times as many classes. So new classrooms had to be built quickly, new teachers appointed, new canteens, etc etc."
And here is the link to the whole thread.