This is a guide ball. He's showing you how to move back and forth but something's wrong...
Press >the green flag< to begin.
Press >C< to clear.
Press >U< to put the pen up.
Press >D< to put the pen down.
Press >E< to stop and get everything in place.
Press >S< to change colour.
If there's something you don't understand then download, or ask in a comment.