What are the windows include folders APIW and APIA used for?
Are there any tutorials on how to use the fasm windows includes in a windows program?

W stands for Wide, the unicode charset which uses 2 bytes per character, it supports all the worlds alphabets. A is for ANSI, the traditional american charset which uses 1 byte per char, it supports only a limited amount of characters.

youll notice alot of different api functions have 2 names, like FindWindowA and FindWindowW. the difference being how you declare the string that holds the buffer. use APIW when calling unicode api functions, A for ansi api functions. i believe microsoft is leaning towards only using unicode in future windows versions

It's worth noting that the ANSI version depends on the OEM codepage/charset...

So, the unicode versions makes your program more useable in other countries? Can all windows functions work with unicode strings? In the examples and includes I looked at, I don't see them used anywhere. I noticed they are functions for various windows system/gdi dll's. Looks like a pretty good job of defining the windows functions, is this all of them, or are there more?

theres no guarantee every windows version supports unicode. most api functions that deal with string buffers have an ANSI and unicode version, only the W function will support unicode. i dont think the fasm package has any included example on unicode. new api functions come out randomly, usually every service pack adds a few. you can use the program here: http://www.dependencywalker.com/ to view all functions a dll exports