Determine a prime number function

//could anyone explain to me the 2nd and 3rd statement in the for loop
//what is the 1st and 2nd i in the middle part and the last one (i = i + 6)

function prime(n) {
  if (n<=1) return false;
  if (n<=3) return true;

  if (n%2==0||n%3==0) return false
  for(let i=5;i*i<n; i=i+6) {  
    if (n%1==0||n%(i+2)==0)

    return false;
  }
  return true
}