It means that you understand what the person has going through. Life is like a journey When you've "been somewhere before" it means you've had the experience before. Person A: "Working so hard late into the night is making me so tired!" Person B: "Been there, done that! It happened to me before!"

James: Let's have some fun. Why don't we go to Disneyland? Mona: Been there, done that. James: Well, then, let's go to that new restaurant on Spring Street. Mona: Been there, done that. James: OK, then, let's fly to the moon. Mona (smiling): Been there, done that -- NOT! James: (smiling): I'll book us two seats on the next flight to the moon.