AppleScript is a rather unusual programming language. Its syntax is very flexible in some areas (it tries very hard to look like English) and very picky in others. It's very powerful in some areas and feels primitive in others.
It's one of those languages where it's easy to read a program, but often hard to write one.
The best way I found to learn it was with a good book, some online guides, plenty of experimenting, and wholesale theft of examples people have posted, to use as a starting point for your own programs.
With some languages, I can write a program from start to finish and it is likely to work. With AppleScript, I always seem to need a bit of trial and error, but that's partly because I use it only when I want to do some little task, and I haven't taken the time to fully master it.