It’s been a long time, but I recall that it was external for my wife. I think you can see the heartbeat(s). They looked like flickering lights on the ultrasounds they used twelve years ago. I imagine things look a good deal more sharp these days. Also in my day, it was all black and white. Perhaps they use false color these days to enhance the display? I don’t know.
They’ll spread some goo on your stomach in the area where they will place the wand. It’ll be some pressure, but it didn’t look uncomfortable to me, and my wife never said anything bad about it.
Good luck! It’s very exciting!