There's a sequence I used to follow when I used Photoshop that I haven't managed to find the equivalent path for in Photo (I'm sure it's there!) and I'd really appreciate it if some kind person could point me in the right direction!
In essence, while on holiday I would take one photo with my wife standing to the left of a sign, then get her to take one of me standing to the right of the sign. Then in Photoshop I would combine them to make it look like we were both in the pic, standing each side of the sign. I did this by stacking the two photos as layers in one file, auto-aligning the layers, then creating a mask to "rub-out" the person-less part of one layer, to reveal the other person underneath. Hope that makes sense!
Looking forward mastering this in Photo, as it's a handy thing workaround when there's no-one else around to take a pic of us both, and I use it quite a bit.
Cheers & thanks