Basically queries the URL with a web request, which grabs the text of a script which then gets piped to Invoke-Expression, which runs said script.
I can vouch for this being legit as I've used it to get Windows 10 LTSC up and running on my current rig, but it's worth taking a look at the script that you're piping to Invoke-Expression before you actually pull the trigger on blindly executing strange code on your machine.
My spergery compels me to yell at you for using aliases outside of the shell.
Basically queries the URL with a web request, which grabs the text of a script which then gets piped to Invoke-Expression, which runs said script.
I can vouch for this being legit as I've used it to get Windows 10 LTSC up and running on my current rig, but it's worth taking a look at the script that you're piping to Invoke-Expression before you actually pull the trigger on blindly executing strange code on your machine.