It's here that you can find links to get more information about developing scripts and add-ins for Fusion. There are also many repositories of sample code written by Autodesk and also links to many community repositories where other developers are sharing their Fusion programs.
For a quick overview of the API you can view a recording of a recent webcast.
You can learn more details about the API by reading the Fusion API documentation.
Also check out these youtube videos:
Note: if you're not a native English speaker then the automatic transcripts/subtitles provided by youtube could be quite useful.
Just click the "Subtitles" icon:
You can also read the full transcript if you watch the video directly on the youtube site:
The documentation is always the first place you should go when you have problems or it's unclear how to use the API.
Need help? Search on forums for similar questions and solutions, or ask your question in a new thread.
We share our solutions, tips and our learning experiences on the "ModTheMachine Blog". Be sure to check it out.