This is how canvas drawing works :
Imagine you're on Paint , or Gimp. You have a mouse/brush (You'll often see context or ctx) and you can say that this brush is a scare (else this is anything) and then fill it or only stroke it.
This how this looks :
ctx.fillStyle = "#000000" //Say your brush is white
ctx.fillRect(0, 0, 100, 150) //draw a rectangle at (0,0) , width 100 and height 150
To draw an image
To draw an animation, you'll have to work with http://atomicrobotdesign.com/blog/web-development/how-to-use-sprite-sheets-with-html5-canvas/
Ok, this is the draw part http://www.html5canvastutorials.com/tutorials/html5-canvas-tutorials-introduction/
Then you have to move all thoses objects. You need a loop, where you'll at each frame update your elements , look for the most used "requestAnimationFrame".
To finish, you have to work with maths, mainly in a pool game where you'll play with vectors.
Good luck, i would have suggested you a pong or something else more easy than a pool game for an html5 game.