Forgive me my ignorance but I am very new to the HTML 5 arena and never worked with graphics using Javascript.

I was doing some reading and came across the Canvas tag and the source stated that the canvas tag acts as a graphics container and is used to render graphics on the webpage by the use of Javascript.

My questions is, why would I need to use Canvas as a placeholder to render graphics instead of using some other arbitrary tag that can be used as a graphics placeholder for example?

A <canvas> tag is exactly like an <img> tag, with the difference that instead of loading the image from the network you can draw it yourself with javascript code. You can draw lines, circles, filled polygons, gradients and matrix-transformed pictures. You can also redraw the canvas content in a loop to make an animation.

To see what you can do with a plain canvas 2d (no webgl, just standard 2d rendering) take a look at this small demo or look at this video if your browser is too old and doesn't support canvas.

It's pure javascript, nothing loaded from the network, everything is computed in the browser, including the texture and the raytraced image used for envmapping part. All in a single 4Kb html file.

Do you really think you can do the same using regular <div>s ?

EDIT:

For a much simpler demo with a readable source you can check out this rotating icosahedron.