The Get-WmiObject command is used to get classes:

Get-WmiObject Win32_Process -List 

The WMI cmdlets are able to recursively list classes in namespaces. The following command lists the classes in rootcimv2 and any child namespaces:

Get-WmiObject -List -Recurse 

In addition to the list parameter, the WmiClass type accelerator can be used:

[WmiClass]"Win32_Process"