This feature allows you to quickly connect with peers on your local network that are in the same transfers or channels. You can find these options in Settings > Transfers > Peers and also Settings > Channels.
Enter one or more IPs in the text view and they will be added to running transfers automatically.
You can use any IP address, private or public, although the feature is intended mostly for use on local networks.
The other options, SSDP Local Peer Discovery and Secure Local Resource Discovery will use UDP multicast on the local network to find peers in common transfers or channels. The Secure Local Resource Discovery is a zero-knowledge protocol that does not reveal what channels you are in to other peers unless they are also in the same channel. The SSDP used for transfers is a standard protocol supported by other torrent clients, but it is not a zero-knowledge protocol, and could reveal what transfers you are in to other nodes in your local network.