Question is a bit broad, but out of all the concepts under the financial engineering umbrella you're bound to explore the concept of ledgering eventually.
I've written a bit about it on my own co's product blog in an attempt to demystify some core concepts [1], [2], [3].
Still on ledgering and expanding into less mathematical and more applied concepts, I can also recommend a book called "The Accounting Game: basic accounting fresh from the lemonade stand" [4].