Digital BW, The Print

I'm still trying to figure this application out.  I do not understand
raw files.  I would appreciate any help on the following questions:

1) are raw files 'naked scans' - i.e., are they influenced by all of
the settings available under the inpug and color tabs?

2) if I am unhappy with a raw scan, it was my understanding that I
could modify it with Vuescan without making a new scan.  If this is
true, how do I get the raw file back into Vuescan?

3)  what is the extension for the raw files? - i.e., are they TIF files?

4)  general question:  what is the difference between the upper and
lower histograms?

Thanks in advance for any help on the above.

Bob