To draw a line on a canvas, we need to:

1. moveTo some starting point.
2. From that starting point, instruct the computer to locate a lineTo an end point.
3. Instruct the computer to apply some virtual ink by performing a stroke.

Here is what it looks like using javascript:

Experiment!

First, try adding a second line.

Then, to do something a little more involved, click on the image above to bring the editor containing the code for the html window displayed on the right. Then, change the value of the variable explain to true to see the result. Note that you should not expect to understand the rest of the code in the html editor at this point, except to note that I added a function call, clearRect(), which erases everything that was previously on the canvas. This way, you can modify the code and make sure that the drawing only includes the code you executed that time.