setTimeout() in draw()

hi,

i'm new to coding and have some problems understanding the setTimeout() and setInterval() functions. I want to use them to draw something every 2seconds. How do i do that?

I tried:
`function setup() {
createCanvas(400, 400);
}

function draw() {
background(220);
setInterval(doit,2000)
}

function doit(){
ellipse(200,200,20);
}`

That doesnt work. I guess that has to do with the loop of the draw-function. Can someone help?

Thanks.