A host is any entity that has an IP address corresponding to a resource of the information system. E.g.: A server, network printer, a NAS server, a temperature sensor, an IP camera, etc.
The list of hosts is shown on page Configuration > Hosts > Hosts.
Monitoring a host
To know the name of the template for a specific Plugin Pack, go to Configuration > Plugin Packs. Search for the Plugin Pack you want, then click on the "i" icon at the bottom left of the pack.
The documentation for the Plugin Pack opens: it will give you the exact name of the template for this Plugin Pack.
Create the host: