One can start softly with the tilt screen. If you have live view / ground glass and shoot wide angles the workflow is really simple:Still getting to grips with the tilt screen.
1) estimate distance to the ground and set hinge distance to that
2) look at live view and see how tall the tallest feature in the scene is, say it covers 50% of the height, adjust the span until it covers that amount, and you get an f-stop. If the scene doesn't have much height at all (say a seascape or something) you can even skip this and just use the app as a hinge distance table and shoot at the ideal aperture directly.
3) set the tilt, focus on live view / ground glass at the middle of the tallest feature, set the f-stop and shoot.
You don't need to use the focus distance / incline setting there as you focus manually. If you have say an ALPA with a HPF ring but no live view it can be nice to calculate the focus distance too though.
Then you can add the remaining features to this workflow as needed. Setting a separate ground distance is useful for longer lenses where you'd want to put the hinge line a fair bit below ground level to avoid having to apply large amounts of tilt that makes the wedge span really narrow. In my Linhof system it becomes useful for say the 72mm and up (~50mm 135 equivalent)
Then there's the camera tilt button which is there to compensate if tilting the whole camera. I almost never use that myself as I prefer to have a level camera and shift instead, and I think most tilt-shift users will do that.
There's also a sharp/soft button here merged into one button for space reasons. The typical tradeoff would be to let tree tops be a bit blurrier if the scene is tight, that is choose a soft edge on the near/upper limit.
The measurement modes are used if you want to measure angles instead of looking at the span directly on live view. This is typically useful for a bit closer distances where angles become a bit larger. For small angles it's hard to measure accurately, and much easier to see/measure on live view. The "span" measurement is the most useful, while "incline" and "hinge" is there for completeness but I don't expect them to be as much used.
There are some issues around hinge parallax when measuring and looking at wedge span, which is discussed in the manual how you handle it. It's generally a smaller problem than one may think though.