These links should help you get started learning about programming with YumaPro APIs.
Server APIs
The API Quickstart has an overview of most the server callback interfaces.
A callback function has to be registered at init time and unregistered at cleanup time.
These details are specified in the YumaPro Server Overview:
The yp-system library allows many system-level APIs to be added to the server at boot-time. These APIs are not related to specific YANG objects.
Client APIs
The yp-shell program within the server can be programmed with custom CLI show commands, using the yp-show library.
The yp-client library can be used to create simple C++ client applications using yangcli-pro session features.
NETCONF over SSH and NETCONF over TLS sessions can be managed, and yangcli-pro functionality accessed from a custom C++ program.
YumaWorks documentation is freely available on our website: YumaPro SDK Documentation.