DNS Servers are mandatory in order to configure services linked to a domain, such as a website or an email address.
The provider of each of these services will provide you with the required configuration details to correctly setup the DNS services for your domain.
Please remember that DNS and Domain Registration are two separate services. It is not mandatory to use the same provider for both services.
A domain can be registered with provider A et DNS services attached to the domain can be those from provider B.
Alias: DNS servers
A set of name servers are attached to any domain. They are part of the domain data, such as the owner and the expiration date.
The nameservers attached to a domain must always be specified at the registrar with which the domain is registered, regardless of who is providing the nameservers.
A minimum of 2 nameservers are frequently required although it is often possible to specify a few additional ones to provide more redundancy.
When a nameserver is not available for whatever reasons, an other nameserver is automatically used instead to resolve the services attached to a domain.
Although nameservers are usually labelled with either a number (e.g. nameserver 1, nameserver 2) or a specific name (e.g. primary nameserver, secondary nameserver), nameservers can actually be specified in any order at the registrar managing the domain.
A zone acts as a container encapsulating all the configuration for a given domain.
It exists a one-to-one relationship between a zone and a domain.
One and only one zone is required to setup one domain.
Consequently, a zone is sometimes simply referred as a domain in the context of DNS Services.
DNS records are grouped under several types. The most popular types are A and MX records.
An A record allow to specify the IP address of a website. MX records are used to indicate the mail servers used for routing the emails.
Basic DNS offers allow to setup to setup the most common types of DNS records. Advanced offers allow to setup a wider range of record types.
Advanced offers may also offer some special configuration techniques to get around to some inherent DNS limitations.
The setup must only be performed once. It is automatically replicated on all the nameservers.
They must be setup at the provider of the nameservers.
When nameservers attached to a domain are replaced by new nameservers, any existing DNS records must be manually recreated on the new nameservers.
The set of all the DNS records configured for a particular domain are usually referred as being the DNS Zone for that domain.
In other words, the setup for a domain consists of one DNS zone which contains all the DNS records.