How to run and control the turtlebot2?

Step1: type 'roscore' in a terminal.
Step2: open a new terminal and type 'roslaunch turtlebot_gazebo turtlebot_world.launch'.
Step3: enter the directory where the file 'interface.py' is, and run it. (You can change the variable 'speed' and 'steer' in the python file, otherwise the turtlebot won't move.)

What we need to do?

Write some codes between 'input' and 'output', to realize some function.