You can use "man <command>" the same as in nix. The man command is an alias for Get-Help and it retrieves the same information.
There's a lot of nix aliases for Powershell commands. Get-ChildItem is also called with ls, mv calls Move-Item, cd calls Set-Location, etc. They made at least some effort to make it more accessible to people coming from *nix or cmd.
Also, unfortunately, you'll probably want to Update-Help first, because for reasons beyond my comprehension, PowerShell does not ship with detailed help installed by default.
