changes
The changes
command is informational, it doesn't do
anything to a checked-out project, but it tells you something about
it.
This is simply a quick way to get a list of the files which are different in the source tree (the checkout) and the repository.
There is a bit more information (was a file edited, added or removed?, for instance).
The same information will be displayed if you
fossil status
,
except there will be some additional repository information displayed
first.
See also: fossil status, Reference