If they can send you a png file, hopefully it will make the edges transparent. If they give you an .esp file it will work with Illustrator and you will need to export it so that it will work with Photoshop. Do an internet search for "exporting a file to png format in Illustrator" and I'm sure you can find several videos on how to do it.
I do have a tutorial where I show how to add a logo to a template.
This is a tutorial on how to add a logo to a backdrop.