How do i setup yearly subscritions?

Hi, very simple question

How do i create 1 year recurring memberships?

Is it enough to use existing levels that have only monthly subscribers BUT link an order button that rebills yearly?

What i dont understand is how does s2member know if a member is for a month or a year

When you create the button code, you should set the duration of the period.
Here is an example with the Paypal button

The same thing is for other payment processing or other periods.