Referencing Variables Question

Hi,

Can someone please explain to me what is the use of the @ sign when referencing a variable in Workbench?

For example: /process_data/@myVar

Sometimes you need to use it, sometimes you don't, sometimes Workbench adds it for you but you shouldn't be using it, I'm confused.

If you have a link to the online help explaining this, that would be awesome.

Thanks

Nic