The "Add Root" menu entry will allow you to create a new root for your address space. A root is a placeholder in the database that is used to group address blocks together. There must be at minimum one root for IPv4 and one for IPv6, since the two address families cannot be mixed.
HaCi will automatically create roots when performing some operations, like importing from a configuration file, although in most of the cases it will ask you if you want to use an existing one. It is possible to move addresses from one root to another.
When adding a new root, you will be asked for a name and an optional description. You will have to decide if this is an IPv4 or an IPv6 root. You will also have the possibility to assign permissions for this root to your user groups.
Please note that no actual address space is defined at this time, you will do that with Add Network.