2. go to the overlay section, and choose 'your own'
3. select a photo and make it the good size
4. Erase the edges, so you won't get harsh edges over your photo.
to get smooth melting edges go to the eraser section and put the hardness on zero and the eraser size on the max. than carefully eraser the edges. if you accidentally erased to much than press the brush button and fill up the gap you made.
6. add more!
add as much overlays as you like
7. Save. if you're satisfied with the end product save it.
I hope its clear. If you have some questions feel free to ask in a comment below.
I'd really like to see what you have made. let your creativity go wild.
I made my own constellation using this technique: