What does the motor support (in %) indicate?

The support indicates the percentage of your own power that the drive unit gives you. In Turbo mode, this is up to 400 percent. This means that if you pedal at 100 watts, the drive unit will add 400 watts for a short time. In Eco mode, you get 60 percent support, which means that when you again pedal with 100 watts, you get 60 watts from the motor.