void setup(){
 size(800,500); 
}

void draw() {
// This is where all the drawing is done.

size(800,500);
background(0); // Uses standard RGB (0,0,0)

stroke(255,255,0); // Stroke colour using standard RGB.
strokeWeight(10); // Stroke width.
smooth(); // Anti-aliasing.
fill(255,0,0); // Standard RGB.
rect(10,10,200,250); // Position from the top left followed by the size.
}