I'm glad to see you here, Sarah. The Add pay period option is used if the separate bonus you'll pay your employee is given based on a specific date range. I'll share more information below.
Adding a specific timeframe will enable you to identify when the bonus distribution is for. If the bonus isn't based on a period, you can uncheck this option so it won't show in the bonus paycheck and proceed with the pay date.
Feel free to read this article for detailed information: Pay employee bonuses.
To help you wrap up this year's payroll and prepare for the next period, check out this article: Year-end checklist for QuickBooks Online Payroll.
Keep us updated if you have additional queries about preparing a bonus-only paycheck. We'll be willing to lend a hand. Take care, and have a good day.