A VPN (Virtual Private Network) is a technology that creates a private tunnel over the internet. All your online traffic is redirected to the VPN server. All data passing between your device and the VPN server you have connected to is securely encrypted. This means that your internet service provider (ISP) and anyone else spying on your traffic cannot see your data. Your ISP is still needed to connect you to the internet, but all it does is connect you to the VPN server. After that, it cannot see which other websites you visit or other internet resources you connect to. For the more techy of you out there, the VPN server acts as a proxy.
A traditional VPN can affect the user experience when applied to wireless devices. It's best to use a mobile VPN to avoid slower speeds and data loss. A mobile VPN offers you a high level of security for the challenges of wireless communication. It can provide mobile devices with secure access to network resources and software applications on their wireless networks. It's good to use when you're facing coverage gaps, inter-network roaming, bandwidth issues, or limited battery life, memory or processing power.
That attitude to the safety and privacy of personal data creates an enormous online security risk. Public Wi-Fi networks, which are ubiquitous and convenient, are unfortunately also highly convenient for attackers looking to compromise your personal information. How do you know, for example, that "starbucks_wifi_real" is actually the Wi-Fi network for the coffee shop? Anyone could have created that network, and they may have done so in order to lure victims into disclosing personal information over it. In fact, a popular security researcher prank is to create a network with the same name as a free, popular service and see how many devices will automatically connect because it appears safe.