Proxmox VE Wiki
The primary source of information is the Proxmox VE Wiki. It combines the reference documentation with user contributed content.
Community Support Forum
Proxmox VE itself is fully open source, so we always encourage our users to discuss and share their knowledge using the Proxmox VE Community Forum. The forum is fully moderated by the Proxmox support team, and has a quite large user base around the whole world. Needless to say that such a large forum is a great place to get information.
Proxmox Server Solutions Gmbh also offers commercial Proxmox VE Subscription Service Plans. System Administrators with a standard subscription plan can access a dedicated support portal with guaranteed reponse time, where Proxmox VE developers help them should an issue appear. Please contact the Proxmox sales team for more information or volume discounts.
We also run a public a public bug tracker at https://bugzilla.proxmox.com. If you ever detect a bug, you can file an bug entry there. This makes it easy to track the bug status, and you will get notified as soon as the bug is fixed.