Although there are 3rd party editors available, you don't need any external software to write, compile or run AppleScript scripts. OS X comes bundled with the AppleScript Editor, which you can find on your startup disk at /Applications/Utilities/AppleScript Editor.app.
Two widely recommended books for those just starting out with Applescript are
Apple Training Series: AppleScript 1-2-3
Sal Soghoian (Author), Bill Cheeseman (Author)
Learn AppleScript: The Comprehensive Guide to Scripting and Automation on Mac OS X
Hamish Sanderson (Author), Hanaan Rosenthal (Author)
These are available from large online book retailers and distributors in electronic and print format at quite reasonable prices (at time of writing they're around $20-$25 each). Each is a substantial volume that will serve both as tutorial and reference work.
There are many other books available, but I can personally recommend both the above as highly valuable. 'AppleScript 1-2-3' is probably the better of the two if you are new to AppleScript and to computer programming in general. It is one of the few computer books I've come across that genuinely lives up to the promise of 'no previous experience required'. 'Learn AppleScript' covers some more advanced topics and treats some of the same topics in more depth. The two books are best seen as complementaries rather than alternatives.
Apple provides some free resources, the most useful of which is:
The AppleScript Language Guide
There is an inconspicuous 'PDF' icon at the top right of that page which will allow you to download the entire guide in PDF form, which may be more convenient than reading the online HTML version.
The AppleScript Overview
may also be of interest, though it is largely aimed at developers wishing to make their apps scriptable with AppleScript, rather than for those using AppleScript for scripting. However, if you would like or need a better conceptual understanding of AppleScript and how it fits in with the entire OS X ecology, this will be of interest.
Getting Started with AppleScript
You may often find references in Apple documentation to something called "Getting Started with AppleScript" but without a link.
This, and pretty much all other public domain documentation for AppleScript, has been collated on an third-party (i.e, not hosted, supported or endorsed by Apple, Inc.) site here:
OS X Technologies is the ASC forum for most AppleScript questions,
but they also do appear on the Developer's forum too.
Perhaps the largest active community of expert and novice AppleScripters alike can be found on the Apple AppleScript mailing list:
A useful external resource both for problem solving and general reference is
The following site also lists a number of useful links and AppleScript resources:
Using 'do shell script'
One of AS's biggest strengths is its ability to incorporate shell scripts through the 'do shell script' command. However, this is often a source of frequent questions from new scripters. See this article for reference on the ins-and-outs of using shell scripts with AS:
Distributing your work
How do I protect my source code?
If you distribute your app without creating a 'run only' version, others will be able to see and modify your source code. To create a 'run only' version use File > Export... and change the File Format: to 'Application'. Check the 'run only' option at the bottom of the dialogue. Note that in earlier versions of the AppleScript Editor and as stated in some of the learning guides above, the 'run only' option was found in File > Save As...' . That is no longer the case.
How do I set the version number for my public releases?
How do I create an 'Application Support' folder for my app?