Follow The Steps -:
1) Download Cracked FaceNiff
2) Once the app is downloaded, install it and then connect the Wi-Fi of your victim.
3) Open the faceNiff app and press the start button on the top. If it ask you to allow permission for the app, do so.
4) It will now be monitoring activity. Anyone who uses Facebook, YouTube, twitter, amazon on the network you are connected to will show up on your phone. Simply click on them and you will be logged in into their account.
Note: It might take 2-3 minutes to load up the screen. So have patience.
If nothing is showing up, try using stealth method in FaceNiff. Some rooters prevent these kinds of hacks; stealth method will attempt to bypass this.