whats the difference and how do i initiate each?
A volume snapshot is a snapshot on a single volume. This is initiated in the volume details window of the GUI.
A volume collection snapshot is a snapshot on all volumes which are part of the collection. This is initiated in the volume collection details window of the GUI.
so volume collections are just the protection plans and they are the only way to do data consistent snapshots.
VSS for SQL or Exchange
Vcenter (whats that do? vm snapshots?)
and the normal snapshots are just point in time, no safety..
it would be really cool if schedules could be once with a time, and immediate
That's correct - a collection is a logical grouping of volumes to allow for a consistency across all volumes at the same time (ie in a SQL environment you would want to ensure all SQL logs and DB were snapped together).
Retrieving data ...