changing file permissions

[norman]

This may seem a very elementary question but it has me puzzled. I made
some changes to a file using sudo gedit and saved the file. Because the
action I was hoping for did not happen I looked at the file's
permissions and found that in the execute box there was '-'. I read up
on how to change permissions and did sudo chmod u+x filename 'enter' but
the '-' did not change. What do I need to do to get a tick in the box,
please?

Norman