What is best settings for witcher III with this setup?
intel I5 4460
MSI Radeon 7950 Black Edition 3GB/384bit
8gb of ram memory?

Resolution 1080p,samsung lcd tv as monitor and hdmi cabal conection.

Thats for you to decide. What exactly do you want? 30fps? 60fps? Somewhere in between? Or do you prefer high visual fidelity with no regards to the cost?

Hm i think at least medium should be fine, maybe high, depending on how many fps you want. I played on a 5870 on medium. It doesn't require much processor power but often used a bit over 8gb memory here, could be that this is a limiting factor, not sure how much influence this has though.

I want to enjoy in nature to slowly ride a horse :-)
I want to be as more beautiful graphics
Fps is not important.