I have felt (and sometimes still feel) your pain
I started out with the FileMaker tutorial. Then the Missing Manual, then FileMaker Training Series. After that, I looked thru the starter solutions. From there I started building my database then either asked questions about something specific, or researched scripts/functions as needed. Doesnt hurt to ask questions about a specific process, turns out there will be more then one way, and the very experienced users/developers here are great help.
Make sure you get FMAdvanced if you haven't already. Then learn to use the Debugger and Data Viewer effectively.
One excellent printed reference is:
FileMaker 12 Developer Reference, by Bowers, Heady, Lane & Love, from Que Publ.
It focuses on Functions and Scripts, and is a valuable reference to have examples of how each script step and function works. I keep my copy within arm's reach. I don't believe a FMP13 version of it exists, but the changes since 12 are very few.
Also, try taking apart the scripts in some of the starter files which come with FileMaker Pro, to see how they work. Reverse engineering some scripts takes some work when they aren't fully-commented, but it's good for learning stuff.
My best advice is comment your script, by that I mean list out the steps you wish for your script to do as comments, then place the script steps in between. When you are finished, then not only is the task of the script completed, but it is also commented so you can see what you were thinking when it was written. Many programming students learned this technique as "pseudo-code".
This process helps you organize your script and not get too lost inside the code.