The payments for yearly (paid monthly) plans and the monthly plans get charged once every 30 days. The yearly subscription gets charged in full upon purchase, and then again in twelve months.
The yearly (paid monthly) plan is billed once every 30 days, for 12 months, while the monthly plan is billed once every 30 days. The yearly plan bills once a year.
The advantage of the yearly plans is that the annual plan price per month is significantly lower than the monthly plans, essentially giving you free months over a 12 month period compared to the monthly plans.