The camera has two memory areas -- inbuilt (usually not very much) and removable card memory.
In most cameras, if you insert a card the camera uses that and ignores inbuilt. Remove card and the camera stores new pix on inbuilt.
Similar when you connect the camera to computer -- with card in the computer can't see the camera's inbuilt memory. At least this is the case on my Olympus.
So if you want to access pix on inbuilt memory without removing the card or want to store the pix to card so that they can be read from (say) an external card reader or picture frame device, you need to transfer pix from internal memory to card.