The same way your house and car keys open your door or unlock your car, USB keys plug in to your computer's USB port to obtain access. If the password and the key match, you're authenticated. If you remove the key, access is revoked. If someone borrows your key, unless they know the password or PIN, it's probably nearly impossible to gain access. While the USB key makes good sense, the design calls for a hub.
Most desktop computers have USB ports in the back, where they're hard to access.
A hub that brings additional USB ports to the front of the computer makes the key insertion easy, and also simplifies the addition of such other USB devices as keyboards, scanners and printers. Hubs that provide additional ports or even serial or parallel ports are also available. To grant system access, these verify your identitty by checking a unique physical attribute, typically a fingerprint. However, thumbprint scanners, retina or iris scanners, even face readers or voiceprint systems are being developed. During set-up, the biometric device first reads the user's fingerprint, for instance, that it uses for authentication.