I want to create a basic form in HTML+JavaScript, how to create it?

Here's a HTML form created by me, JavaScript (snowing) I took from Internet

```js
     function myFunction(){
        var canvas = document.getElementByName("vardas");
        alert(canvas);
console.log(canvas);
    }

    window.onload = function(){
     //canvas init
     var canvas = document.getElementById("canvas");
     var ctx = canvas.getContext("2d");

     //canvas dimensions
     var W = window.innerWidth;
     var H = window.innerHeight;
     canvas.width = W;
     canvas.height = H;

     //snowflake particles
     var mp = 100; //max particles
     var particles = [];
     for(var i = 0; i < mp; i++)
     {
      particles.push({
       x: Math.random()*W, //x-coordinate
       y: Math.random()*H, //y-coordinate
       r: Math.random()*4+1, //radius
       d: Math.random()*mp //density
      })
     }

     //Lets draw the flakes
     function draw()
     {
      ctx.clearRect(0, 0, W, H);

      ctx.fillStyle = "white";
      ctx.beginPath();
      for(var i = 0; i < mp; i++)
      {
       var p = particles[i];
       ctx.moveTo(p.x, p.y);
       ctx.arc(p.x, p.y, p.r, 0, Math.PI*2, true);
      }
      ctx.fill();
      update();
     }

     //Function to move the snowflakes
     //angle will be an ongoing incremental flag. Sin and Cos functions will be applied to it to create vertical and horizontal movements of the flakes
     var angle = 0;
     function update()
     {
      angle += 0.01;
      for(var i = 0; i < mp; i++)
      {
       var p = particles[i];
       //Updating X and Y coordinates
       //We will add 1 to the cos function to prevent negative values which will lead flakes to move upwards
       //Every particle has its own density which can be used to make the downward movement different for each flake
       //Lets make it more random by adding in the radius
       p.y += Math.cos(angle+p.d) + 1 + p.r/2;
       p.x += Math.sin(angle) * 2;

       //Sending flakes back from the top when it exits
       //Lets make it a bit more organic and let flakes enter from the left and right also.
       if(p.x > W+5 || p.x < -5 || p.y > H)
       {
        if(i%3 > 0) //66.67% of the flakes
        {
         particles[i] = {x: Math.random()*W, y: -10, r: p.r, d: p.d};
        }
        else
        {
         //If the flake is exitting from the right
         if(Math.sin(angle) > 0)
         {
          //Enter from the left
          particles[i] = {x: -5, y: Math.random()*H, r: p.r, d: p.d};
         }
         else
         {
          //Enter from the right
          particles[i] = {x: W+5, y: Math.random()*H, r: p.r, d: p.d};
         }
        }
       }
      }
     }

     //animation loop
     setInterval(draw, 33);
    }
```

```css
    body {
     /*You can use any kind of background here.*/
     background: #6b92b9;
    }
    canvas {
     position: absolute;
     display: block;
    }
```

```html
    <!DOCTYPE html>
    <html>
    <head>
    <title>forms</title>
    <meta http-equiv="Content-Type" content="text/html" charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" type="text/css" href="mystyle.css">
    <script src="demo.js"></script>
    <canvas id="canvas"></canvas>
    </head>
    <body>
     your name:<br>
     <input type="text" name="vardas"><br>
     <button type="button">Click Me!</button>
    </body>
    </html>

```

The form is created but I can't write on it.