Usually , we can log into the NVR as the default account “admin” , then access all functions in the NVR.

But if you enable the option "Enable Double Authentication"，it means for accessing some special functions, it will ask you to login with another account to enhance the security. 

 take "Playback" as an example :

1. enable "Enable Double Authentication"

2. go to "play back ", it will ask you to enter another user authentication.

3. go to create a new account "test"

now you have 2 users 

4. then go back to the "playback", and enter "test " to pass the verification.