Invoke-Item (which has an alias, ii) has a number of different uses. Invoke-Item will open or execute an object using the default settings for that file:

Invoke-Item .   # Open the current directory in explorer 
Invoke-Item test.ps1   # Open test.ps1 in the default editor 
Invoke-Item $env:windirsystem32cmd.exe    # Open cmd 
Invoke-Item Cert:# Open the certificate store MMC for the current user 

The registry provider does not support Invoke-Item.