this is what you want?

function drawSquare(canvas, context, color){
    var x= Math.floor(Math.random()*canvas.width);
    var y= Math.floor(Math.random()*canvas.height);    
    context.fillStyle = color;
    context.fillRect (x,y, canvas.width, canvas.height)
 }
 
 let canvas=document.getElementById('canvas');
 drawSquare(canvas,canvas.getContext('2d'),'pink');

<canvas width=300 height=300 id="canvas" ></canvas>

Your question is very vague.

What technologies are you willing ( or able in the case of homework like project) to use to achieve your goal?

If you have no idea how to do it then i would suggest you start learning of some jQuery, that is a javascript framework, that allows you to do some pretty cooll and easy stuff.

If you do end up using jquery, all you would have to do is to create an element lets say:

<div id="container"></div>

and then somewhere in your javascsript you would have a javascript array with the objects that you are rendering for, say an object named square { color,title,text,name,this,that }

And after that you could just create a loop,construct your html elements as string and use jquery to append the elements in your DOM. An example would be :

var myContainer = $('#container'); <--- this holds a reference to the container element using jquery
for(var i=0,len=myArray.length;i<length;i++){ <-- in my array you would have your "square" objects so that you can modify each square based on parameters like name,title,color etc
    var elementInString = '<div class="square" style="color:"'+myArra[i].color+'>';   <-- and create your parameterised square here
    $(myContainer).append(elementInString);
}

This is one way to do it. Other way include using other frameworks (Knockout,Angular etc)

I hope this helps

If you use jquery it's really a simple thing to do:

$("#your-button-id").click(function() { 
   $("#your-square-parent-id").append('<div class="your-square-class">&nbsp;</div>');
});

But you can do that without jquery as well as Joseph stated above. Anyways, hope it is useful.

In your code, Math.floor should be within parenthesis instead of square brackets like:

let randomNumber = Math.floor(Math.random() * 3);

Then you should get the element by id from the squareRND like:

document.getElementById(squareRND).style.backgroundColor = randomColor

You should also run the colorChange();

For example:

let button = document.getElementById('button');
const changeColorOfaRandomSquareToRandom = () => {
  //This I hope will pick a random square
  let randomSquare = () => {
    let array = ['square1', 'square2', 'square3'];
    let randomNumber = Math.floor(Math.random() * 3);
    return array[randomNumber]
  };

  // I assign the value of the randomSquare function to a new variable
  let squareRND = randomSquare();
  console.log(randomSquare());
  //This picks a random number
  let rgb = (num) => {
    return Math.floor(Math.random() * num);
  };

  //This picks a random color
  let colorChange = () => {
    let randomColor = 'rgb(' + rgb(255) + ',' + rgb(255) + ',' + rgb(255) + ')';
    document.getElementById(squareRND).style.backgroundColor = randomColor;
  };
  colorChange();
};

button.onclick = changeColorOfaRandomSquareToRandom;

#square1 {
  background-color: lightpink;
  width: 200px;
  height: 200px;
  display: flex;
  margin-top: 200px;
}

#square2 {
  background-color: lightblue;
  width: 200px;
  height: 200px;
  display: flex;
  margin-top: 200px;
}

#square3 {
  background-color: lightgreen;
  width: 200px;
  height: 200px;
  display: flex;
  margin-top: 200px;
}

#squares {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

#button {
  width: 75px;
  height: 25px;
  margin-top: 20px;
  margin-left: 600px;
}

<div id="squares">
  <div id="square1">
  </div>
  <div id="square2">
  </div>
  <div id="square3">
  </div>
</div>
<button id="button">Click me</button>

In ES6 you can do the following with Exponentiation (x ** y), which produces the same result as Math.pow(x,y):

function squareIt(number) {
  return number ** 2;
}

console.log(squareIt(5));

or you can use a JavaScript library called BigInteger.js for the purpose.

alert(bigInt(5).square());

<script src="https://cdnjs.cloudflare.com/ajax/libs/big-integer/1.6.40/BigInteger.min.js"></script>