Confused need help!

[Sprut_UK]

It does also depend on how you present the part to the cutter..............if you can safely tip the part on it's side you can then produce the radius quite easily as a 2D cutterpath. This is assuming that it is a radius around a single plane........if it is say a torus (doughnut) type shape then this will have to be done using 3D machining.
If it's not possible to use this method and the radiused face is facing the tool, then machining it as a 3D shape is your only option.
The uppermost part in your image looks like it has rounded edges.........these can be done using a radius cutter following a 2D shape, or, you can 3D mill it using a ballnose cutter.

I have created this short video to help you visualise the differences that I am referring to. The first part shows the part being machining in 3D and the second part shows the same part being machined using a 2D strategy:

http://www.download.sprut.co.uk/MyCNC/2D-3D/2D-3D.html

I hope this helps?

Dave