VPS (Virtual Private Server) hosts are comprised of several isolated server environments hosted on one larger partitioned server. A VPS functions essentially as it's own standalone server since each user will have root and full control over everything running on their environment.
As far as support goes, it will essentially be handled the same way we handle our dedicated servers. cPanel clients will have fully managed support and clients who do not choose a control panel will have limited support (i.e. hardware, major operating system issues, etc.)