what is the key step of "merging" two images?

[Krikor]

(05-14-2021, 01:02 PM)kenny1999 Wrote: I'd like to cut a face of someone and paste onto another, they have different skin colors
of course. After selecting and cutting the face, what is the next step to do? 
Would you please highlight me the key steps I'll probably need?

Among the possible technical options, one is shown in the video: https://www.youtube.com/watch?v=2e6FikWMkaQ