FileMaker Help has a reference with all script steps and functions.
Books on FIleMaker is another good source. Have a look at this one:
linda.com has some tutorials: FileMaker Pro Tutorials | Lynda.com
Also, look at the resources on the community forum. There are a few things like this:
Here is the link to the script reference resource nicolai was referring to:
It's very useful.
I'd also recommend the companion reference PDF for functions:
Thank you Nicolai,
Thank you Beatrice,
The help section of filemaker is also a great resource as it explains how to use every script step and function in enough detail for you to get started. I would start looking at the starter solutions and FM Starting Point by Richard Carlton Consulting (and any other free, unlocked, solutions you can find ) to see how all the pieces can fit together.