When the PHT_EVENT object is used as an event data container, a handle to it is obtained through callback functionality (a handle is passed as a parameter to a callback function). When the object is used as an extended error information container in asynchronous functions, a handle to it is obtained from the PHT_JOB object returned by a function by calling the PrlJob_GetError function. 

The common steps in processing an event in a callback function are as follows:

1. Determine the type of the event by calling the PrlEvent_GetType function passing the event handle to it. The event types are defined in the PRL_EVENT_TYPE enumeration. This will tell you what happened on the Virtuozzo Service side. For example, a virtual machine state has changed, the host configuration has been updated, etc.
2. Determine the event source by calling the PrlEvent_GetIssuerType function. The function returns the event issuer type that you can look up in the PRL_EVENT_ISSUER_TYPE enumeration. This will tell you if the event was generated by the host, a virtual machine, a web service, etc.
3. If an event was generated by the Virtuozzo Service or a virtual machine, you can obtain the server or the virtual machine handle by using the PrlEvent_GetServer or the PrlEvent_GetVm function respectively. Depending on the event type, you may use a handle to access the Virtuozzo Service or a virtual machine and perform some operations on them if needed.
4. An event object may contain additional parameters, which can be retrieved from it using the PrlEvent_GetParam function. The function returns a handle of type PHT_EVENT_PARAMETER containing an individual parameter data. There may be multiple parameters in a given event object, so the function must be called once for each of the available parameters. To determine the number of parameters, use the PrlEvent_GetParamsCount function. Once you've obtained a PHT_EVENT_PARAMETER handle, you can use its functions to retrieve the parameter values.