If would like to know how I done this on my phone: (Note I'm not a professional)
Step Zero. Must have an android.(Unless these apps are also on IOS I'm unsure..)
Step one. Find background that you'd love to use.
Step two. Find some pictures you'd like to make transparent of the background.
Step three. Download this https://play.google.com/store/apps/details?id=com.handycloset.android.eraser (This will take some time but once you understand it, it is easy! I use to make assassin logos all the time from my phone & other things with this and the next one I'm about to tell you about lol)
Step four. Download this https://play.google.com/store/apps/details?id=com.handycloset.android.photolayers (This allows you to place a background and then add whatever pictures you want added into it)
Step Five. Use some sort of editing app that gives you your effect you want of the picture(such as filters or brightness, etc)
Step Six. You're done!!
Now if there are some other sort of apps someone else might be using to edit please feel free to let me know! Thanks!