VirtualTraining enables to connect the classic trainer + speed sensor and based on the known trainer's power characteristic VT calculates the virtual power. The resistance must be controlled by user manually, but VirtualTraining calculates the virtual power and convert it into virtual speed. VirtualTraining supports most of the classic trainers, for sure check the compatibility list.
Virtual Training calculates the virtual speed to be able to compare the results cross all users and trainers. Read more about how the virtual speed is calculated here.
App needs to read the current speed from the external speed sensor. Speed or Speed/Cadence combo sensors communicate via both ANT+ and Bluetooth Smart protocols, some support one protocol only. Please, check the documentation to your sensor what protocol is supported. Based on protocol and the platform you can check what all accessories you will need to connect sensor (for classic trainer) with Virtual Training.
Do you need to connect via Bluetooth Smart?
Do you need to connect via ANT+?
How to connect the trainer in App?
If you have all accessories / fulfil the hardware requirements, you can connect the trainer in App. See more for specific platform.
Do you want to know what the hardware minimum requirements to be able to use Virtual Training? Read more in system requirements.