The add extension option is used to create a user which can be used to register an IP phone or softphone to the following extension. This is the first feature that you will use after you have created your account.
To add an extension you will need to login to your MyIntegra then go to Hosted VoIP >Manage >Devices & Number >Devices >Extensions. Then click the new button.
As you can see, within extension settings here are just a few settings of many which can be configured for your hosted VoIP device. For example the description of the extension can be changed to the name of the person that is going to be using the VoIP device, as well as the length of the ring time which can be increased or decreased in multiples of five. Then we have the MAC address of your device, if you have a deskphone then the MAC address will look something similar to the address displayed in the example below.