Yeah, this one could use a bit of explanation. Powerful tool, not sure we did the best job of describing it.
First, the setup. There are two sets of settings, one for airports and one for runways, because when you're going generally to the airports, you're might be more comfortable with steeper approach guiadance and/or descent rates.
When are each of the above settings active? When you're on a flight plan to an airport, it uses the airport settings. When you're direct-to a runway (new v15 feature), it uses the runway settings.
The vertical-speed oriented settings are hopefully self-explanatory enough. They drive the magenta line guidance.
The angle setting drives the blue line guidance.
Now what do each tell you?
The magenta line is the vertical speed you need to maintain "right now" to get to the target you defined in setup. If you have a flight plan, it follows it so that it takes any extra distance into account.
The blue line is telling you what vertical speed you'd need to maintain to fly the glidepath through space you programmed in setup. It doesn't care about the airport, runway, or any terrain. If you fly the VS it's marking, you're flying the angle programmed. The blue line guidance only shows up once you're in a descent of at least a hundred feet per minute (not positive on the number), too.
So what falls out of this is, if you put the magenta line on the blue line, and then fly that vertical speed, you'll fly a perfect X degree glidepath to the airport or runway. And this next part isn't that obvious, but if you treat the blue line a reference point, and the magenta line as glide path needle, you can fly the magenta needle just like you would a conventional glideslope. IE, if magenta is above blue, keep holding your altitude. You're not targeting any specific VS at this point. Eventually the magenta will settle onto the blue. Then, put your airplane's VS on the lined up bars, and you're on glidepath.
