enable grouping of computers from the same LAN or, more importantly, from different LANs - often in different physical locations, into a separate network with the same properties as the common LAN.

equipment

The only equipment required are the switches that support this functionality. Their configuration is software based.

benefits

Allow logical grouping of computers that corresponds to the organizational structure. 

Provide increased security by limiting access to resources only to the members of the particular VLAN.