Exelwebs.com will NOT place ads on your site. That is one of the many advantages of having a paid host.
We do have a default 404 page that can be replaced in a few seconds with your own that we recommend doing to help maximize your traffic.
If you aren't sure how to do this open a ticket with us and we will be happy to do it for you.
A 404 page is what loads when someone visits a page on your site that doesn't exist.