Those cryptic symbols are enhanced modifiers for referencing batch variables. Microsoft explained their use in the link you provided so there is no need to repeat it. Generally they allow you to create substrings of defined strings (ie: getting the file extension from a full file name).
While they have their uses, they tend to reduce the readability of batch code. WinScript is still a better way to go.
I think the're only valid on XP and 2003 Server.
Hope this helps.