You'll just need to mask the layer you wish to turn into a transparent well using the masking tools of course such as the magic wand, the brush & erase tool.
- If using Superimpose you'll save it under "Mask as PNG".
- In Sketch Club you'd save as PNG (Transparent) just be sure to not have a background in the overall save.
- Photo Wizard Lite you'll save Mask.
- And using Photoshop you'll mask out, and make sure there is no background you'll know by the grey, and white squres, and just save as PNG. (Visit thetransparents tab for free transparents.)