GIT: how do I update my local copy?

[Allan Duncan <amd2345 fastmail com au>]

Git may be a very powerful tool for kernel developers, but I can't see how
to get the equivalent to svn's operation:

"git clone" makes a local repository, except that the timestamps are for
the time of the clone, not those of the source repo.

If I want to get any changes made to the original repo, what is the
command needed?  I tried a few likely ones, but can't crack it.  My current
workaround is to rename the local repo and do the clone again, then try and
find the changes.

I tried rtfm, but it is a bit terse and overwhelming.  A GSG might help.