Terms you'll need to understand:
Contiguous namespace
Disjoint namespace
Domain
Forest
Global Catalog
Global Catalog Server
Organizational unit (OU)
Schema
Site
Tree
Techniques you'll need to master:
Understanding the design elements that make up Active Directory hierarchy
Understanding the function of each design element in Active Directory
Selecting a naming scheme to be implemented in an Active Directory design
Identifying the two types of namespaces available in Active Directory: contiguous and disjoint