Hai Tom,
Controlpoint and control line are marvelles tools.
Starting with control point which was called Upoint.
Think of it as a eye.
Pupil, that’s the place you select the pixels you want to effect/select.
Red? The mask search for red pixels.
Iris,the circle around it, that’s the complementary colors, if those are contrasting the feathering got harser. (Use [M] to see masking i like black and white more then the new masking color which is less detailed in how much it bin effected. It’s more a colored plain of which part of the image is effected.
And 3 the eyeball, the resizeable circle.
The bigger the circle you drawn the more feathering you get and the more area you effect.
When they added luminance and chroma control you got a very powerfull masking tool.
Chroma is how much of the wavelength of red for instance is selected.
Full left is almost all color full right is only like the selected pixel color.
(if i remember correct,y, i haven’t used pl much lately because my pc is too slow the cope with my impatience editing images…
i build a new one of my christmasbonus i think.)
Negatives you can use to deselect parts of the selection.
Before the luminance masking was made this tool was the place to get close to that.
My advise keep it in black and white masking feature and play with all the sliders and possibility’s, move the pupil around on the place and see the white and gray and black change. Move the sliders chroma and luminance to see it’s effects on the masking.
The link is a example of how far and manny you can use… As a fun editting moment.
The control line is great for skylines and sky’s.
Or to use it to get more dehaze on one part over the other.
Like enhance detail on treewood and leave the leafes more hazy/blurred like the wind in a forrest image.
Or enhance parts of sunset without effecting the foreground too much.
Remember in 50/50 slider it’s like the first upoint, color and luminanced based selection in pin point.
You can zoom in place the marker on a few pixels of your choice, extend the outer circle ,the eyeball, and zoom out to stretch that cirle even more. It’s much more versatile then most people thinks.
Like smart lighting the power is in how you use it.
If you have more questions there is a great online usermanual written by @Pascal which give with examples how the control are working
(i hope he’s dropping the link for you. 
)
And you can drop your problem image and dop file in this thread and point out on what kind of problem you get stuck.
Then others can go back and forward on your editting to see uf they can solve the puzzle.
Have fun…
An old post after i thought about how to use the upoint technology even more…
Dxopl is evolved more and the luminance masking is part of that.
Hue colorwheel another, color softproofing is added, and much other things profi users where used too have in adobe like productes.
Like LUT’s and such. Imho too much choice in tools/presets to effect toning.
Best way is use preset editor and partial preseteditor to make your own named presets. From the one’s dxopl offers you with your twist over it.