You can use it to evaluate the ArchiCAD Application Programming Interface (API) without any registration required. However add-ons developed without registration will be loaded only by the DEMO version of ArchiCAD.
Once you decide to be a Registered 3rd Party Developer please contact Graphisoft at http://www.graphisoft.com. Upon registration you get your developer ID and authorization key, which enables you to create "real" add-ons.
GRAPHISOFT SE ("Graphisoft") LICENSES THE ENCLOSED SOFTWARE TO YOU ONLY IF YOU ACCEPT ALL OF THE TERMS OF THE LICENSE AGREEMENT. PLEASE READ THE TERMS CAREFULLY BEFORE STARTING THE DEVELOPMENT. IF YOU DO NOT AGREE TO THESE TERMS, GRAPHISOFT WILL NOT LICENSE THIS SOFTWARE TO YOU.
ONLY REGISTERED DEVELOPERS ARE ALLOWED TO USE THE SOFTWARE FOR COMMERCIAL PURPOSES.
Refer to the Add-On Management document for further details.