It will help users to block any unwanted user to log in into their account. The unique feature of this service is that it will use an application to do so as compare to the previous method in which user have to sent a SMS to confirm the log in. The new method will provide an end to end security and there is no role of any third party.
How it will work
1.Users have to download Twitter application and install into their device and it will generate a 2048 Bit RSA keypair, which will store the private key into your phone and sends the public key to the Twitter's server.
2.Now whenever there is a new log in request the server sends a challenge ID which is 190 Bit random nonce.
3.It also provide users with time, date and location for the requested log in.
4.Now its all depend on users if they want to approve or deny and if they approved it then it will ask them with the private key and gives the information to the server.
5.Now server will compare the challenge with a request ID and if it authenticates the account will automatically logged in.
Users can also make a back up of the key but remember to put this into a safe place as it is the second way to log in into their account if they have forgotten their private key.
Users can go to the ME tab in the application, open setting and then tap on Security and turn on the log in verification. And if you are a user using Android then you have to tap on your name.
Hope it will help you and if you have any confusion you can ask here.