What is a VPN? why we need VPN? what is a Vlan tagging?

AVPN is a Virtual Private Network deployed over public facilities that provides similar levels of privacy, security, quality of services, and manageability compared to networks built entirely on dedicated, privately owned or leased facilities.

Virtual private networks (VPNs) provide enterprise-scale connectivity on a shared infrastructure, often Ethernet-based, with the same security, prioritization, reliability, and manageability requirements of private networks.

VLAN Tagging, also known as Frame Tagging, is a method developed by Cisco to help identify packets travelling through trunk links. When an Ethernet frame traverses a trunk link, a special VLAN tag is added to the frame and sent across the trunk link. As it arrives at the end of the trunk link the tag is removed and the frame is sent to the correct access link port according to the switch/router table, so that the receiving end is unaware of any VLAN information. 

VPN is virtual private network, which create to extend features of  private LAN network beyond the physical boundries or your can say extend across the globe or over public infrastructure, service provider backbone. VPN is used to secure your confidential traffic over public network.

VLAN Tagging is the practice of inserting a VLAN ID into a packet header in order to identify which VLAN (Virtual Local Area Network) the packet belongs to as in switch network we segregate the department with respect to their functional responsibility on the basis of VLANs.