Hello Dawn
The add-paths is used when you have multiple paths from the hub to a specific network that can be reached via multiple spokes. EIGRP however advertises only one path as the best path to connected spokes. The add-paths command allows EIGRP to advertise up to an additional four. This will only be seen if multiple paths are present to the same network.
For the topology in question:
As can be seen, there are two routes to the 192.168.12.0/24 network, via Spoke1 and Spoke2. The hub will have only one route to this network by default. The add-paths command will allow both the Spoke1 and Spoke2 route be added in the routing table.
More information on the add-paths command can also be found at this Cisco documentation.
I hope this has been helpful!
Laz