Just typing Get-Command will give you a full list of cmdlets (PowerShell commands), alias, and functions.  Typing Get-Command -CommandType All or Get-Command * will give you a list of all commands including .EXEs in the path and .DLLs

Get-Help is a cmdlet that give you a detailed description of how to use cmdlets, functions, providers, alias, and anything else that has a help file.  Get-Help * will give you a list of all help files and Get-Help -Category HelpFile will get you all of the about_ files that describe how PowerShell works.

man is an alias to Get-Help which makes getting help quicker and more familiar to Linux users.