Simple from single sender to multiple receivers. Network nodes duplicate data as it passes trough it.
1) IP Addresses
2) Internet Group Management Protocol (IGMP) used to discover listeners on local network
3) Protocol Independent Multicast (PIM)
4) Distance Vector Multicast Routing Protocol (DVMRP)
5) Multicast Open Shortest Path First (MOSPF)
6) Multicast BGP (MBGP)
7) Multicast Source Discovery Protocol (MSDP)
8) Multicast Listener Discovery (MLD)
9) GARP Multicast Registration Protocol (GMRP)
10) Shortest Path Bridging (SPB)
I know that those a links to Wikipedia. Temporarily only, with time I will replace those with my version...