Name scoping
Names declared in outer namespaces can be used unqualified within inner namespaces.
Here, the names Middle and Class1 are implicitly imported into Inner:

namespace Outer
{
namespace Middle
{
class Class1 {}
namespace Inner
{
class Class2 : Class1 {}
}
}
}

If you want to refer to a type in a different branch of your namespace hierarchy, you
can use a partially qualified name. In the following example, we base SalesReport
on Common.ReportBase:
namespace MyTradingCompany
{
namespace Common
{
class ReportBase {}
}
namespace ManagementReporting
{
class SalesReport : Common.ReportBase {}
}
}
[/quote]

I'm not at all following what he's talking about even. Could someone explain this in a more beginner friendly manner?