In your case it would probably be like this. . .
md $ENV:USERPROFILE\Documents\WindowsPowerShell\Modules\Get-Freespace
The open that folder in explorer. . .
invoke-item $ENV:USERPROFILE\Documents\WindowsPowerShell\Modules\Get-Freespace
In that empty folder copy your get-freespace.ps1 file and change the extension to psm1
-VERN