Net working: it is number of system connected together physical and logical, what are phasical and logical compenents ?

Physical are the real components of the network such as switches , routers  firewalls etc

one switch can be devided into logical groups called virtial (LAN)Local Area Network  dividing the users into several groups but uses the same switch, examples  sales vlan is uses by the sales staff, engineering is used by technical staff etc.