How to make my mobile robot stop using sensors?

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Hi,

I'm new to Gazebo & ROS and currently working on modeling a mobile robot in order to simulate its movement indoors. I had no problem with urdf, adding joints, sensors, actuators all done. There are two things that I haven't grasped yet (I have basic knowledge in cpp):

1- while adding a sensor plugin, what part of the cpp file makes the connection between that specific sensor and the code? and how the plugin name and filename related to the code? (I wanna make my own plugin).

2- when I move my robot using teleop_twist_keyboard is there a way to make it stop on its own before an object like modifying sensors node or creating another node specifically for this?

Thank you