I got my CCENT and working on ICND2 to get my CCNA. I am stuck on this topic and am unable to grasp the context. WAN and VPN and how they differentiate. My understanding is we need WAN for "Physical" connectivity between different locations so we can connect our private LAN's in addition to go out to the internet. With just a WAN link, all we can do is just go out to the internet or if we have a routing protocol set up we can ping each routers public IP addresses.
Then with VPN we use that existing WAN setup to create a virtual network so that our private traffic generated from our LAN's can communicate and exchange info. For example a user in the local office is retrieving a file from a private server on the Corporate office, this action is not possible just with a WAN link and a VPN is needed. Am I getting it right? Is WAN alone just for public traffic and VPN allows private traffic over our public WAN. Basically what can I do with just a WAN link and what can I do with just A VPN and do we almost always need both working together. Thanks for your help!