What’s the difference for prepaid cell phones?

My family is looking for two phones, are first cell phones. On T-mobile it has a plan for prepaid phones, Unlimited Text and $0.10/minute. Link: http://www.t-mobile.com/shop/plans/prepaid-plans.aspx?WT.mc_n=PrePdPlnsOvrMain&WT.mc_t=OnsiteAd
Does it have to be pay as you go? I’m not sure I understand. Can someone clarify?

A prepaid mobile phone is a mobile phone for which credit is purchased in advance of service use. The purchased credit is used to pay for mobile phone services at the point the service is accessed or consumed. If there is no available credit then access to the requested service is denied by the mobile phone network. Users are able to top up their credit at any time using a variety of payment mechanisms.