Zen sits on the sofa across the room and stares at me. What does he want?
If I ask him "what do you want?" he cannot answer me in words. But he can still tell me. How? By what he does.
If he jumps up, grabs a toy, and deposits it in my lap he has just clearly communicated his current desire to me. Let's say I'm busy and don't want to play right at that moment. So I tell him "go lay down" and he heaves a sigh of disappointment, but goes back to the sofa and settles into a relaxed down to nap for a while longer.
I used my "go lay down" cue and he completely understood what it meant. He didn't like it, but he understood it. We had clear mutual communication.