Extensions are short three digits numbers plus two digits branch prefix. Within the same branch you do not need to dial the prefix. If you do not use branches all extensions are created in the default branch.
Extensions can be assigned to:
Users (it makes easier to dial manually from a device)
Call park – extension is needed for direct pick up
Call group
Group intercom
Extensions are shown in the Settings\Numbers menu.
When adding a new extension choose a branch of leave default if you do not use branches. Then define extension number - has to be unique within branch. Next choose the route type and select the route object.