Does anyone know where i can find source code of turtlesim package?

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I want to understand how this simple simulator works. I can't find any good explanation. For example, in ros_tuturials they say: 1. run roscore 2. rosrun turtlesim turtlesim_node 3. rosrun turtlesim turtle_teleop_key

But how it's connected? how it works? (I know there topics,master, etc.). and what about measure of speed? speed unit = ? (metres per second) . Is there a motor(simulation of it) or it's just moving on the screen from one point to another point?

A lot of questions...

Any ideas, guys?