Most of the documentation for the bilevel measurements panel can be found here: Scope Bilevel Measurements. The results are averaged over what is visible in the display, so if you want the measurements about just one edge, zoom in on just that edge. If your signal is noisy, you may have better results setting your high and low state levels manually (use the "Settings" tab in the Bilevel Measurements dialog).
For settling time, you'll need to set the minimum duration of time that you expect the signal to completely settle out. For example if you are measuring the settling time of the rising edge of a positive-polarity pulse with a width of 50 ns, you can set your settling seek duration to something like 40 ns.
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