With regard to backgrounds, if you don't want it to be visible ensure this is transparant. You'll usually see this as a grey and white "checkered" effect when opening the file in any popular design software such as Photoshop.
NOTE: A white background is NOT transparant . If you see it in the background of your design once you've upload it this is what will be printed!
You can easily make the background transparent within the Designer App, All you need to do for example is click the "select transparent" button underneath the Design Properties box and choose the colour you wish to make transparent.
If it's white (it usually is) slide the RGB sliders all the way to the right making each one 255, then click "Select"
This should delete the white and make transparent! Remember, you'll need good artwork for best results!!
You can do this for any other colour too. (It's best if you know the RGB values though to be exact!)