Documentation
There is extensive AutoIt documentation available and this documentation is your recommended reference. If you have AutoIt installed then you can find it in the SciTE editor if you press F1, or in the start menu under AutoIt > AutoIt Help File. Many developers keep the documentation or AutoIt Help File, as it is better known, constantly open to look up functions and keywords.
Offline
An offline copy of the help file is available for download on the official AutoIt home page. You download the AutoIt Full Installation or the AutoIt Self Extracting Archive which both contain the AutoIt help file.
Using the help file
There are three common methods of using the help file. You can use either the categories to browse the help file, use the index to search for document titles and use the search function to look in the entire page.
Either one method is good and works well for a variety of situations. As an alternative to the search method, you can use Google to search in the online documentation which generally works better.
Still can not find an answer to your problem? Use the forums.
Source
The source code for the help file is available to anyone so that they can expand, modify or translate the original. After editing, the help file source code can be submitted to the development team.
Online
There is also online documentation available if you do not have or want to download the offline version. This is less convenient to use for regular development since some features that the offline help file offers are not supported.
The online copy can be found here: Online documentation
If you like to try AutoIt Online in your Webbrowser you can use script-example.com free AutoIt Web Compiler
Searching
Similar to the forums, you can use Google or your search engine of choice as a valuable searching tool. You start your query with site:http://www.autoitscript.com/autoit3/docs/ and then your search query.
A finished query may look like:
site:http://www.autoitscript.com/autoit3/docs/ GUICtrlCreateButton
Function list
Additionally, a list of all the functions exists on this Wiki. It is not maintained as regularly, and is redundant to the previously mentioned methods. You can find it on the Function list page.
Other languages
The AutoIt help file is available in a few other languages beside English. Almost constantly translations in other languages are being written.
You can find these help files here: Non-english documentation