Controlling motors in ROS Kinetic on Raspberry Pi 3B

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Hello,

I'm new to ROS and I followed this video https://www.youtube.com/watch?v=iLiI_...

I did not use the exact same car but a simple car with a servo motor and a DC motor instead.

At 9:00 of the video, he started to publish some topics but I don't know what servo 1 and servo 2 mean, I have no idea where I should connect the motors to the Raspberry Pi.

Please don't mind my dumb question and thanks for any help.

Some spec:

Raspberry Pi 3B

Ubuntu Mate 16.04

ROS Kinetic