A USB ANT+ dongle is what receives the signals from the sensors on your bike or your trainer and transmits them to your computer and Zwift.
Getting an ANT+ dongle is easy. Head on over to the Zwift Shop to pick up a handy starter pack or check out our friends at Competitive Cyclist or Wiggle! Any USB2 ANT+ dongle will work. We recommend the USB-m as it has proven to have the best signal reception in the lab. Make sure you pick up a USB extension cable to get the dongle closer to your equipment and prevent dropouts.