The two sections are for the two different modes of the render engine: PhotoReal or Interactive. Unless you have changed it you are likely using PhotoReal as it is the default, so the Interactive doesn't much matter. However, what it means is: you are telling the render engine what devices to use in each mode. GPU is the best option, CPU and GPU is a secondary option allowing the renderer to use both the GPU and CPU to render (I don't recommend CPU and GPU, there are many mixed reports of its stability and efficacy; your mileage may vary). OptiX is a ray tracer enhancement and it is highly recommended.