Apple has an excellent online documentation library for AppleScript programming. This can be found at The Apple Developer Connection.

Learning the Language

• Basic commands
• Numbers and strings
• Lists and records
• Aliases and paths
• Scripting other applications
• System Events
• Shell Programming
• Script Libraries

Command Lists

• Advanced Code List
• Standard Additions
• 3rd Party Codes

Sample Programs

• Mail alert
• Archive selected mail
• Run QuickTime in full screen
• Converter for temperatures
• Letter Replacer
• Calculator
• Safari Quit Warning
• Create new Word doc and insert text and format text
• Create a unique email address
• Guess The Character Game

Tip: If you can't find help for a problem from here, you can try searching with Google. For example, if you are searching information about how to use command repeat, write into the text field words "applescript repeat" (without quotes). Usually there should be helpful page amongst the first ten results.

See the Wikipedia article AppleScript for more info