In the File Input section, upload a .zip file that contains the images to be used in the collage (only .jpg's will be used). Then, in the Text Input section, create the message you would like drawn with the images. You can also change the size and scale of the message using the other fields. When you're all set, press Generate. If you wish to cancel the request, press Cancel. Also, to reset the page to its default state, press Reset.
At the bottom of the page is the Preview section, which will give you an idea of how the generated image will look. The preview is drawn to scale and will update automatically as you change the message.