Armoured cable is normally used to transfer power either underground or overhead. The construction is normally the inner cores (which are generally multi strand) being individually sheathed, then covered by an initial overall plastic sheath, followed by the protective wire armour with a final outer sheath to hold it all together. The inner cores may number two, three or four depending upon the application.
The wire protective armour should always be earthed at one end to ensure that it cannot become live if a fault should develop within the cable. Wouldn't think there is any need for a pipe, but seeing as you already have it in place, well and good.
The inner cores mean we can make other uses out of the cable e.g run a light/socket to the shed.