Hello Suhaib, I hope you're doing well!
To get started with Zigbee 3.0 stack development, I would recommend you read this document right here, it details the basic concepts of the stack, and it also contains more important information related to Zigbee PRO APIs.
You can find more information, examples, and other related documentation about Zigbee 3.0 in this page right here.
Please, feel free to ask me any other questions you may have.
Best regards,
Sebastian