You can train new judges by having them judge competitions without their results being included in the official judging.
When you assign a website judge to a competition by using the "Judges" button on a Manage Competition page for a competition, you can indicate that the person is a "Judge in Training".
A "Judge in Training" is someone that will judge a competition as a training exercise. The judge can score and critique images, but those values will be hidden from all, except a person with the "Mentor Judge" role. The judging results will not be used when computing scores and awards.
A person with the "Mentor Judge" or "Competition Manager" role is able to review all judging by using the website menu "Judge", "Judging Queue for Website Judging". That page display a list of the current competitions eligible for judging or recently judged. You can click "Analyze Judging" on a competition to review how judging was performed and review how a "Judge in Training" evaluated the images.
The role of "mento Judge" is assigned using your website menu "Administration", "Manage Members". Use "Edit" on the person and click "Edit Roles". Check the "Mentor Judge" to assign them that role.