I ran across a fantastic article over on The Copy Paste Blog that had listed WordPress cheat sheets you can print out and reference so you can easily know not only what files do what in WordPress, but learn how to leverage some hooks, functions and more for customizing your WordPress theme or possibly designing a new theme from scratch.
The basic WordPress files in the first doc are common, but many themes now reference quite a few custom files which can confuse the average user. There can also be page templates (which are custom template files for unique pages) which can grow your theme file list considerably.
Still, I found almost all of the docs very valuable and even after working with WordPress for 2 years I didn’t know all the php snippets and functions without having to reference or search for them on the WordPress Codex. I have myself downloaded and printed out the sheets to hang on my cork board.
You can find more details and print out the 10 WordPress Cheatsheets from The Copy Paste Blog and I highly recommend you download them and get more familiar with how WordPress works. This can help you with tweaks for your own themes and is good knowledge to have.