The & operator tells you where a variable lives. If int x = 5, then &x gives the address where 5 is stored. This works with any variable type. Print addresses with cout: cout << &x prints something like 0x7ffc4a8b2c.
The exact address changes each run. What matters is you can access it. I'll use this operator constantly with pointers. The & symbol means "address of" before a variable name. It takes different meaning when declaring references.