Simple interest is principal times rate times time. The interest does not earn interest. A two-year loan at simple interest costs twice the interest of a one-year loan at the same rate. That is different from the compound-interest page, which applies the rate to the growing balance.
$10,000 at 6% simple interest for 3 years earns $1,800 of interest. The amount owed at the end, if nothing was paid along the way, is $11,800.
It does not amortize a monthly payment, and it does not compound. Use the mortgage or personal-loan page when the balance should be paid down each month.