This will be so anticlimactic when it happens. First "message" will be some sort of beacon to get our attention. Unless we win the powerball alien lottery, they will be hundreds if not thousands of light years away. So it will be we have detected and alien beacon, we are sending a response and will hear back in hundreds if not thousands of years. That will be it for anyone living at the time. Any interesting communication will come a long long time after we are all dead. Aliens are not going to be transmitting anything interesting initially, just some signal that stands out from the background so it can be detected.