Powershell, created and developed by Microsoft, is a useful scripting language compatible with all major operating systems, with its several hundred modules, each one with several unique cmdlets, memorizing all of them, is a next to impossible task, so knowing how to find help and syntax guides is a key skill.
Outside of the CLI, there are a few websites with lots of useful information.
docs.microsoft.com/en-us/powershell/
This is the official product documentation for Powershell distributed by Microsoft. It has setups, sample scripts, tutorials and other tools.
powershell.org
Created by the The DevOps Collective, Inc to give educational opportunities to members and a forum to discuss and get help.
powershellgallery.com
A central repository for sharing and acquiring Powershell code including Powershell modules, scripts, and DSC resources. If you need a module and help with it.
Within Powershell there are also a cmdlets to obtain information and see what is available.
Get-Module -ListAvailable
Find out what is available
Get-Help
Get help for commands. For example: Get-Help Get-Help
Get-Command
Gets all the commands related to a module or command. For example: Get-Command Get-Help -Syntax
or
Get-command -module ModuleBrowser
Show-Command
Opens a new window with a command builder.