Sometimes you will need to test more than one thing at a time. The logical and operator (&&) returns true if and only if the operands to the left and right of it are true.

The same effect could be achieved by nesting an if statement inside another if:

if (num > 5) {
  if (num < 10) {
    return "Yes";
  }
}
return "No";

will only return "Yes" if num is between 6 and 9 (6 and 9 included). The same logic can be written as:

if (num > 5 && num < 10) {
  return "Yes";
}
return "No";