In Zabbix, a "host" refers to any physical or virtual device, application, service, or any other logically-related collection of monitored parameters.
Creating hosts is one of the first monitoring tasks in Zabbix. For example, if you want to monitor some parameters on a server "x", you must first create a host called, say, "Server X" and then you can look to add monitoring items to it.
Hosts are organized into host groups.
Proceed to creating and configuring a host.