The billing is explained at the time of your upgrade, but I'll copy and paste it in here for you.
Initial upgrade for a profile requires 12-month advance payment that instantly grants access to the above features for the next 12 months**. The charge will appear on your credit card statement as SI Online. On 9/1/2014 monthly payments of $2.90 will begin and continue on the 1st day of each month until cancellation. You may cancel this upgrade at any time.
"Don't give up, the beginning is always the hardest." My Mom:)
Once cancelled, no further charges will occur unless you decide to upgrade your profile again.
"I'm happily indifferent to the ones who have consistently been wrong" ~kd lang~