AD is install on a computer this computer called Active Directory Domain Controller ADDC.
Object are categorize
1) Container Objects : container objects can contain other objects and create collection. Example Forest, Tree, Domain and OU.
Example Of Container Objects
1) Organization Unit (OU) : OU is a smallest Container object and admin can create a small container in a Domain. When admin can separate or categorize the Users then create OU.
Following Work we Create OU
i) Can Apply GPO.
ii) Create sub Security boundary.
iii) Apply software and policies.
2) Domain : Domain is a Collection of Objects or logical group of computer who use Active Directory. Domain is represent by the triangle.
3) Tree : Tree also a container and collection of one or more Domain. There are a relationship between Domains. Like Parent and Child and use Namespace.
Domain A TRISON.com and Domain A parent of Domain B
Domain B Market.TRISON.com