You can set your subscription price between $1.00 and $50 per month, or between $1 and $500 for a yearly describtion, or you may set your account to be a free subscription.
Select your Avator (the top left little icon on your screen) and click on "Edit Profil" and head over to the "Pricing Setting" Tab.
You can there set your Acount to be a paid subscription and set the pricing, or set the slider to an "unpaid" subscribtion.