The Kodak Retina was my dad's first ‘proper’ camera which he bought himself. Later on I got it and learned the technicalities of photography with it.
While being simple, the camera is just perfect for this kind of learning as you have to do all relevant steps manually and get a feel for them in the process: You measure the brightness using the metre at the top, you choose an exposure time and the camera adjusts the aperture when you set the brightness value. Of course you have to manually focus as well by setting the distance to the object.
After doing that for a few films, the relationships between f-stops, exposure times, and ISO numbers which people often consider to be mystical as they include concepts like inverses and squares (that strange are seen as very sophisticated these days), you just have the whole number work ingrained. Just the fact that you see and set all the numbers and that you can adjust – literally feel – them mechanically makes everyting very natural.
With its 55mm f2.8 lens the camera is reasonably powerful and it even includes things like a bulb exposure mode, an exposure timer, the ability to multiply expose a negative, an image counter that goes backwards and the ability to attach a wire release.
What also amazes me is how far a good bit of standardisation can go. Films, mechanical wire releases and tripods still come in the same shapes and sizes many decades past, making this camera a useful tool even today.