im a little confused as to how you can name the variable in the 'for in' whatever you want 'prop in person)

// Here I have an object called koala
let koala = {animal: 'Koala bear', cool: true, age: 22}; 

// Now I want to loop through all its properties (animal, cool & age).
// Prop is the property in the for...in-loop, and koala[prop] will give you the value of that property.

for (let prop in koala) {
  // Here I am console.logging the property first. In the first loop it should be animal, second it should be cool and so on.
  // Then I am adding the value after, I'm looking inside the koala-object and giving it 
  // the "key"-value of the property.

  // So first loop says in just strings "animal: Koala bear". Because the first property is animal. 
  // When I'm looking up the value its the same as saying koala[animal]
  console.log(prop + ': ' + koala[prop]);
}