A typical function definition in the specification looks like this:
CK_DEFINE_FUNCTION(CK_RV, C_GetObjectSize)( CK_SESSION_HANDLE hSession, CK_OBJECT_HANDLE hObject, CK_ULONG_PTR pulSize );
This defines a function named 'C_GetObjectSize', the return value of which is of type 'CK_RV'.
It takes three arguments:
An overview of all functions is presented in chapter 11 of the specification.
What functions, mechanisms and operations depends on the module that is used, and what state it is in. Refer to the documentation of your specific module for more information about this.