Nameservers are used to tell web browsers where your Domain is hosted and mail servers who's handling the email services for your Domain so you can receive email based on your Domain name (firstname.lastname@example.org), etc. You will need to specify the correct Nameservers at your Domain Registrar in order for your web hosting and email services to work properly with your Domain.
For example, West County Media's Nameservers are:
Your Domain's Nameservers are managed wherever your Domain's DNS is managed, and this is typically your Domain Registrar (eg. GoDaddy, Network Solutions, Namecheap, Google, etc.) which is the company you paid to register your Domain.
West County Media provides full Domain Registrar services so you can easily Register and Transfer Domains from within your client account at https://my.westcountymedia.com.