Hello @Sohil-Farahi ,
Active Directory Domain Services (ADDS) is a directory service that stores information about objects (users, computers, etc) and makes this information easy for administrators and users to find and use. It provides authentication and authorization for a domain environment.
Domain Name System (DNS) is a service that resolves fully qualified domain names (FQDNs) into IPv4 and/or IPv6 addresses.
ADDS relies on DNS to function, (how users locate logon servers, etc) so when you install ADDS, it will ask you if you want to install the DNS role also. If you already have DNS running on your network, you don't have to install the DNS role.