Where do the codes reside when I install a ROS package using apt?

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I have recently installed turtlebot3 packages on my system using the apt package manager. But when I go into the package 'turtlebot3_teleop' I dont see any codes or anything. I just see a folder called 'launch' supposedly where all the launch files reside and a cmake file. I wanted to know where are the codes which make the turtlebot3 subscribe to the values I publish through my keyboard keys? Also where are the codes for the nodes which run when I run the launch file?

I have some idea that these packages are installed as binary packages, hence only their executable form is visible, but I don't have much clarity about this.

Pls explain

TIA