Pixels per Tile:
Drop the Tile images here.
To generate a Mosaic image:
1) Drag and drop the images which will be used to tile the image into the blue area.
2) Drag the original into the canvas area.
3) You can change the Pixels per tile using the pull down menu if you desire.
4) Press the Generate Button.
You can repeat the process over and over adding more tile images and changing sizes etc.
You can save the generated image just by right-clicking on it and selecting save.