Help understanding the lens/camera settings

Hello,
I was going over the camera settings in Blender and found that there are some I just don’t understand.
So I set it to a full frame 35 mm camera. That is easy to understand as it sets the sensor size.
Not to sure what auto does on the sensor but I have it set to horizontal and that is fine.
Then comes the Depth of Field settings.
Focus point is the eyes, just fine.
Viewport? what is that anyway?
I clicked high quality as it sounds good but what does it really mean?
Then comes F-stop and I have that at 2.0, thinking it would be like a normal lens set at f-2.0 and 9 blades as that is what the best lens have.
Then comes Aperture??? What the heck is that? It seems to work like the F-stop and the F-stop on view does not change anything in the 3d view when set to cycles rendered. And the number again? What is it compared to the sensor size and the Veiwport F-stop? Then we have blades once again. So I am confused. I would think that Viewport is just for the 3d rendered mode but it does not change anything there but Aperture does. I would guess that aperture is only for a final render, is that so? So what give?

Thanks for your help. I find this all rather confusing.

The viewport f-stop is for the viewport dof (when enabled in the properties panel under shading)

For camera settings see https://docs.blender.org/manual/en/dev/render/cycles/camera.html

Yes, that is what I thought too but it does not seem to work that way.

With default cube and focus point set to one corner of the cube, viewport dof enabled and small f-stop I get visual dof blurring of the scene