meaning of icons

[norman]

I have been trying to find a list detailing the meaning of the various
icons used with no success. Some are obvious and some are not. For
example, I want to open a file and I am refused. When I look at the file
in the folder it has a lock on it. OK, the meaning may be obvious but
where can I find out what I need to do to open the file? I tried sudo
but that did not appear to work.

Norman