Slony-I needs path information, that defines how a slon process can communicate to other nodes. The conninfo string takes a connect string as described in the libpq connection documentation. Usually, you will need to specify host, dbname and username, while the password should be stored in the .pgpass file.
You must create a path to every other node, on each node. For example, in a two node cluster you need to create a path to the slave on the master, and one to the master on the slave.
After the communication path has been defined, the slon processes need to be advised to listen to events from other nodes.
Note: This step is not necessary for Slony-I v1.1 and later, because listen information is generated automatically when paths are defined.