Sorry, time flies by so quickly.
There are no videos (yet) for the wave editor, mostly because it has been rather basic, but some explanation will surely help, especially since the stretch tools were added.
First, the Range tool. It is used to select a range (well...), when a range has been selected you can apply operations to this range. This includes the operations in the Functions menu but also Copy, Cut and Paste.
If there is a nasty noise it can be cut out, (or tempered by lowering the gain) for instance. Or you can move around a piece by cutting it out and moving the play pointer and pasting it again.
If you have another wave editor that is better at manipulating wave data it can be set up in the configuration to be launched when you select the Edit in External Editor... menu alternative to edit the bit selected in the Range. Audacity is an obvious choice but be aware that Audacity makes it a bit hard to save the wave file back with the same name (which MusE relies on to get the edited wave back). Another good editor is Ocenaudio (not open source though).
Then we have the Stretch and Samplerate tools. I had to do some tests here as this functionality is not finished but they /can/ be used, and are very powerful for what they provide.
A heads up is that they are not affected by Undo/Redo, not sure if this is by design or if it is not finished, but it can be a bit confusing.
Stretch and Sample rate work the same way but alter the audio either by changing the pitch or changing the length. Well, both change the length but one of them does not change the pitch... uh, this is hard to explain, easier to try maybe
When one of the tools are selected you can click on your wave form and add lines that later can be moved. To remove a line if it ended up on the wrong place, click on it and hit the delete key. There are no menu alternative or button that I know of yet.
Also good to know is that you can right click on the wave form and a menu alternative containing Converter settings appears, in this dialog a lot of alternatives are available, I'm not sure how much of this is working, most of it I think. I think it is missing a detection what actual support libraries are installed so I think it gives options for editing algorithms that might not be installed.
I think a good way to use the stretch and Sample rate is to add atleast three lines. The middle one is the one you adjust, the other two are the start and stop of the range that can be affected. But this might very well be depending on use case.
So, that's most of it I think. I read your other question also and will try to respond to that later.