cg clears graphics

do cg will clear all graphics drawn.

do cg

It will clear all graphics drawn with pens and dots, but it will not clear text written with write, and it will not clear turtles made by new Turtle. See ct and cs to clear text or clear the whole screen.

Saying cg by itself will not do anything, because our language only runs commands with at least two words: you need to use do cg.