Help with Integration Processes (ccBPM)

Please help me to understand Process Container variables and "instance of process". I don't quite have a handle on the concepts. Thanks.

When a message is sent to an Integration Process and it is a reciever/start message, is a new process instance instantiated to process the message?

Say another message is sent to the same Integration Proces, is another instance created (ignoring correlating)?

My last question is whether the Process Container variables are Process Instance specific?

Thank you for any help.