How do prepaid cell phones work?

I want to get the lg neon tmobile go phone

http://www.wireless.att.com/cell-phone-service/cell-phone-details/?device=LG+Neon+%28TM%29+-+GoPhone%C2%AE+-+Prepaid+%28Refurbished%29+-+Green&q_sku=sku3950484

If I get the phone do i just have to pay for the phone, and get minute cards.
Or do i also have to pay at&t an additional cost each month. like 15/month???

it depends on where you are getting it from. if you are getting from the phone holder store itself, you will probaly just have to give them how much you would like to put on it whenever you want minutes on it. if youre getting it from just a store,(like walmart,for example),you will just have to buy a minute card whenever you want to put minutes on it. and,you wont have to pay it monthly. i have had about 4 prepaid phones in my lifetime,so,i hope i helped!