add a counter to my page

There are many web counters out there but you can simply use the one that Vex.Net has installed.  Contact support@Vex.Net and we will set up a counter for you.  You will get a URL which can be treated as an image on your site.

However, perhaps a counter is not what you are really looking for.  If what you are looking for is statistics on how many hits you are getting you may find the web logging and stats generating features more useful.  Check the FAQ entries on those items.