Quick tip: Use the docs!

You just learned how to use a bunch of functions: ellipse, rect, line, background, fill, stroke, strokeWeight, and noStroke.
How can you possibly remember how to use all of them? Don't worry, you don't have to!
Whenever you're programming, you'll have documentation, or docs, for that programming environment that tell you how to use all the functions. On Khan Academy, you can always find the documentation under whatever program you're working on:
GIF that shows scrolling down to the documentation and using a particular page.
The documentation shows you what parameters each function takes, and it also links to a whole page for each function with much more information and an example. If you're scratching your head about anything, make sure you check the docs first.
If you can't figure it out from the docs, don't fret—there's a whole community of Khan Academy coders who can help you, too. Just click "Request help" on your project, clearly describe what you're trying to achieve, and wait to see what they say.