Learning flash with Yongnuo 560IV and other photographer made me more confused. Help?

So, a wedding photographer wants me to work with him as a second shooter and learn from him. I have a Canon t6i, he has a Nikon full frame (don't know the model) and he said he uses the 506 flashes. I understand the 560IV being a manual flash and not TTL, which I haven't tried yet.He says that he's able to see the exposure in his light meter, that includes his flash power, in his camera with the flash being manual. I said that I can't see that in mine because it's manual but he says that it works for him and must be a "Canon thing." Am I thinking about this correctly that you have to know your flash settings and adjust when needed?Thank you for your help and I hope this makes sense. via /r/photography http://ift.tt/2uww7eQ