Cella of a multicellular organisms are specialized. What does this statement mean?

Different Cells do different things

For examole you have Bloodcells which are specialised to transfer everything the organism needs, you have cells which makes nerves which are specialised to send and recieve impluses

Different cells complete different jobs. Though they all contain DNA for every function, stomach cells will never do the job of brain cells and much of the genetic information isn't actually used