In role administration what is the difference between role owner and user owner ?
Also, when we say a role can act as a participant and principal, what does it mean ?
As the wording itself indicates,
Role owner is a Role that is the owner of the current role
User owner is a specific person in ITIM that is the owner of the current role
When it comes to roles acting as participants, you can think about workflows. An example is when you have an approval workflow. Your business rules might say that the for en employee to get a mail account one of the managers needs to approve the request. Let's also assume that you have a Role in ITIM, let's say "Level X Manager" and this has a few members. According to the business rules, if you as an employee request an email account, anyone that has the Level X Manager role can approve the request.
You would model this in an approval workflow, and in the approval node, the Participant entity would be the role "Level X Manager". When you will request the account, ITIM will send notifications to anyone that has the Level X Manager role and any of them can approve the request.