Website created by Sitedudes.com - how to redirect to them? Name Server Change?

My wife's website is hosted with HostPapa - but she contracted SiteDudes.com to design and maintain her website (trying them out). In order to get her new site "live" we're supposed to enter their NameServer info somewhere...can't figure out where. Submitted a ticket to HostPapa late last year but have not heard back. Left a voice mail today.

Does anyone know where I'm supposed to enter the NameServer info to "redirect" her domain name to the SiteDudes.com created website?

Fairly new to webhosting so not sure of the tech terms. Almost seems like Sitedudes is now hosting her website though? Wondering if I need to change the Hosting arrangements with HostPapa...but not sure what that means for her email access through her domain?

Welcome any helpful information

Thanks