The custom Filemaker Google Search is handy
Search for "calculation fields"
Search for "calculated fields"
There is not a lot of overview tutorials that I have seen.
Unless you are looking for design or normalization howto's.
Sometimes you will see articles on syntax. I can't find my list right now.
FileMaker has some good training materials on their website:
I picked up "FileMaker 9 Developer Reference" from Que when I was at the Apple corporate store. I find this a handy reference when I am using a command I haven't used in a while.
Hope this helps,