Promissory notes are contracts and contracts don't make dishonest people honest. A DIY contract is likely a mistake. You can buy a promissory note off of a site like or use a local attorney.
A simple promissory note might be for a lump sum repayment on a certain date. For example, let's say you lend your friend $1,000 and he agrees to repay you by December 1st. The full amount is due on that date, and there is no payment schedule involved.