There are a number of investment books for beginners listed on Amazon. Maybe check a few out and see how they format it and what they do & don't cover:
http://www.amazon.co.uk/s/ref=nb_sb_ss_c_1_23?url=search-alias%3Dstripbooks&field-keywords=investing+for+beginners&sprefix=investing+for+beginners<Added>As it's non-profit and it may include investment products that are time-limted, I would advise putting it out as an ebook - Kindle or Smashwords - so it can be updated annually if you so wish.
<Added>You might also consider adding a disclaimer saying this book does not guarantee investors will make a profit, and the market can go down as well as up, etc, etc.