Viewfinder.

A Rollieflex. A twin lens reflex. 

Which means that what you see through the viewing lens on the screen is not what the taking lens sees. This gets worse the closer the subject is. No problem, there is a parallax correction device (a viewfinder flag that shows where the top of the taking lens frame is). Very clever. 

Focus - sharpen the image on a ground glass screen or use the split image focus aid. There is an essential flip up magnifier. Sorted.

Framing - the image in the viewfinder is the correct way up, however, if your subject in front of you is moving left to right it appears in the viewfinder as moving right to left. It takes some getting used to. For action photography you can look through the square hole in the back wall of the hood, flick up the magnifier and front wall of the hood for a pretty vague framing device, but you have no ability to focus. 

With all the quirks (and there are many many more) this is my favourite camera ever. Most of my favourite photos were taken peering into this viewfinder. 

It produced images that easily matched (if not exceeded) my far more expensive Hasselblad.