Direct answer
For a user diagnosing or configuring a VPN connection, “concepts and operation” means understanding what the VPN is supposed to do (establish a secure tunnel, route selected traffic through it, and often manage DNS) and what must be true for it to work (correct protocol/ports, reachable VPN endpoint, and working routing/firewall on both your side and the network). In practice, you diagnose by checking whether the tunnel is established, whether traffic is actually flowing through it, and whether name resolution (DNS) and routing behave as expected.
How it works (concepts in operation)
A typical VPN connection involves: (1) your device negotiating with a VPN server, (2) setting up an encrypted tunnel using a selected VPN protocol, and (3) directing certain traffic through that tunnel. Many setups also include DNS behavior (either resolving via the VPN or using your local resolver depending on configuration). When diagnosing, it helps to separate “connected” from “traffic is routed correctly”—a client can show a connected state while DNS, routing rules, or split-tunneling settings prevent the expected sites from working.
Practical context for setup and troubleshooting
Start with operating conditions you can control: choose the correct VPN protocol/transport settings (when available), ensure the VPN server endpoint is reachable from the current network, and verify that firewall or security software is not blocking the VPN’s connection. Then verify observable effects: confirm the device’s outward-facing IP changes as expected, test DNS resolution behavior for a domain you can reliably query, and check whether only some apps are routed (split tunneling) or all traffic (full tunneling). If a VPN fails, retry from another network (e.g., mobile data) to distinguish local/network blocking from configuration issues.
Limitations to keep in mind
A VPN does not guarantee anonymity, complete safety, or guaranteed access to content. Performance and availability vary with network quality, device resources, your location, the VPN service, and time. Also, “working” depends on current routing and network policies—what works on one network may fail on another due to firewall rules or protocol restrictions.