do you mean the x10hosting ads, or just any ads.
if you want to add any ads just go to the admins ad section, and follow the procedure there
its very simple, as for x10hosting,
i think you can go to file manager, then open your mambo pages, add the code right after <body> section
and the ads should appear at the top.
just let the site be up for an hour with the ads code, and it will apear after then. (it needs to contact the x10hosting ad server, so it takes a little time)