I would highly recommend the Month of Lunches book by Don Jones and Jeffery Hicks, pretty sure Jeffery writes for Petri. I’ve used it and found it invaluable for learning powershell.
If you don’t want to purchase any books then learn by using. Add the following to your powershell profile and it will pop up with a different command that you can learn about.
Get-Random -input (Get-Help about*) | Get-Help -ShowWindow
Get-Command -Module Microsoft*,Cim*,PS*,ISE | Get-Random | Get-Help -ShowWindow
Here’s the Petri link
and the MVA
PluralSight have videos if your learning method is based around that.
But in all seriousness read the Lunches book and start using by automating some tasks that you do repetitively.
An example i have is using plink to connect to a firewall and pull out the current tunnel statistics to make sure they are up.
Another is using plink to connect to the firewall and backup to a location on my local system.
Both use an external tool but are done in powershell.
For a more powershell centric look at looping through your servers and getting the disks sizes of them.