Cam someone clearly explain why 'int &x' takes the value of a not 'int x'

Question

https://code.sololearn.com/cIeExSgmWR8j/?ref=app

Answer 1

The ampersand is essentially the memory 'address of' the value.

Answer 2

what do you mean?!
u r passing ' a ' into the 'swap' method as the first argument ('int &x')