Honestly, this thing does so little that you should just read the code.
Here's what a game using Atom looks like:
class Game extends atom.Game
constructor: ->
super
atom.input.bind atom.key.LEFT_ARROW, 'left'
atom.input.bind atom.key.RIGHT_ARROW, 'right'
update: (dt) ->
if atom.input.pressed 'left'
console.log "player started moving left"
else if atom.input.down 'left'
console.log "player still moving left"
draw: ->
atom.context.fillStyle = 'black'
atom.context.fillRect 0, 0, atom.width, atom.height
# Carry on.
game = new Game
window.onblur = -> game.stop()
window.onfocus = -> game.run()
game.run()<canvas></canvas>
<script src="atom.js"></script>
<script src="game.js"></script>