Question about topics

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Hello, I just want to clarify some questions about the ros topics using a turtlebot.

If there is a node foo and this node use advertise with a topic bar and after using publish, the information will be sent like foo -> bar. The message is baz and is an stadart message type from ROS.

When bar recieve the message, bar doesnt respond. The questions are:

1) I have to connect only foo -> bar or make something bidirectional foo <-> bar?

For example in the beginner tutorials is the teleop keyboard working good (based on the bringup minimal), but when I try to make a node and publish to the same topic like the keyboard teleop, there is no response from the robot.

2) Where i can find the raw code of the turtlebot_teleop?

I made an echo an the messages are being published good, my subcriptions are the same that the teleop via keyboard to.

3) What could be happening?

Thanks beforehand!