This module adds a second authentication factor after the password is entered, by using a TOPT algorithm (Time based one time password). In this way the user needs to use a helper app in their smartphone to get the second authentication code needed to login to the web GUI.
Once installed a new module will appear under the Security menu, that will enable you to activate two factor authentication for the current loged in user. Once two factor is enabled for the user, the next time you login, you will be prompted for the two factor time based code generated by your phone app. For this authentication method to work, your server time must be set correctly.