Whether you are wanting to sell Ongoing, Fixed term, Paid in Full, or Trial memberships; Checkout pages would be the best way to sell those programs online without you ever needing to manually add them in yourself. You will be able to get your new signups to also both sign their contract/digital agreement and pay their down payment all from their own device taking that manual work off of your hands.
This video will show you all the steps you would need to take to ensure your checkout page(s) are set up correctly and will work as intended 100% of the time.