Open up PicsArt and go to edit. Click any background color you want, but white works better.

Go to tools and click on crop.

Hit ok and pick two photos of any character. I chose these.

Pick one of your pictures and make it cover the whole page.

Next get your other picture and put it over the picture you just put on. Hit blend and swipe to over lay. Change the opacity to 50.

After that you can add anything you want.
This should be the finish product.