Adding New Graphics

The section

 //Load Images in line 83 
game.load.image('platform', 'platform_1.png');
game.load.image('platform2', 'platform_2.png');

is where the images are loaded, ready to be called by the game. The part inside the round brackets

('platform', 'platform_1.png')

could be thought of as saying

var platform = url('platform_1.png');

If you just replace

'platform_1.png' with 'platform_2.png'

you are replacing the image location for "platform" with the image location for "platform2".

You are not loading two separate images that you can load into the game at the same time.

To expand on Brice's answer,

Isagani, the first function 'game.load.image' loads images that can be used in the game. If you want to use both platform images, you need to have these lines. They are located around line 87 under the comment //Load images

game.load.image('platform', 'platform_1.png');
game.load.image('platform2', 'platform_2.png');

Now when you call the function 'platforms.create()' you can pass either 'platform' or 'platform2' depending on which image you want to appear.

Such as:

platforms.create(300, 150, 'platform');
platforms.create(450, 300, 'platform2');

This would place the image 'platform_1.png' at position 300, 150, and then image 'platform_2.png' at position 450, 300.

This is why the teacher added the second 'game.load.image' line rather than just replacing the values passed to the function.

Hope this helps.

-Tom