The canvas is the area where the commands are visualized, where the commands “draw” a picture. In other words, it is the turtle's playground. After getting some code in the the code editor, and executing it using File->Run, two things can happen: either the code executes fine, and will you most likely see something change on the canvas; or you have made an error in your code and there will be a message telling you what error you made.

This message should help you to resolve the error.

You can zoom in and out the canvas with your mouse wheel.