Tom is wondering if it's necessary for him to have a VPN (Virtual Private Network). Leo says if he uses Wi-Fi in public, or he uses networks while traveling, he's somewhat vulnerable because he's on a public network that bad guys can get into. They can't necessarily spy on him, but they could trick him by putting up fake access points. A VPN sets up a connection between his computer on a public access network and a computer somewhere else run by a trusted party. All the data transferred over a VPN is encrypted so it isn't visible by anyone else on that network. Leo even uses a hardware device called the Tiny Hardware Firewall so that no one can even see his machine on the network. Leo has lately become more concerned about dangers of using public networks, but most of what we do is most likely already encrypted online such as banking and email.
On his home network, it isn't as necessary to have a VPN. The only one who can spy on him on his home network is his internet service provider. They can see everything that he does. Some are worse than others when it comes to this.