The 'file' datastore is the filesystem of the computer. It is the only possible datastore for the 'file' protocol: you cannot (and do not need to) create a new 'file' datastore.
It can be used to load and save data from and to any file of the accessible drives or mounted volumes.

A resource in this datastore is a file: a 'file://' URI identifies a file, and optionnally can specify a format for this file, that would override an eventual file name extension.