How do I validate my Pass? What does validation mean?

Validation of your Pass means that the first day and last day of validity have to be filled in prior to your first train trip. Furthermore the box ' Validating Stamp'  needs to be stamped.
You should always have your pass validated prior to your first train trip in Europe. This means, before your first trip in Europe, a Railway official at a ticket window has to stamp your Pass and will fill in the first and last date of validity on your Pass.
It is not possible to validate the Pass yourself.