Summary of a variety of things you may have seen
system variables, global variables and local variables
let statement with many variables on the same line
increment shorthand += and ++
mouseX, mouseY
width, height
windowWidth, windowHeight
mousePressed()
Challenge:
canvas is what you see on screen
graphics is a hidden object similar to a canvas that can be drawn on the actual canvas. It can be drawn multiple times as well.
createGraphics - similar to createCanvas although it is a hidden canvas that can be drawn