Have you ever used a piggy bank to save money for something you really want? Pay as you go phones work the same way!
Instead of having a monthly bill for using your phone, you put money into your account and use it as you need it. Just like adding coins to your piggy bank, you can add money to your phone account by buying a special card called a "top-up" card or by adding money online.
Every time you make a call, send a text message, or use the internet on your phone, some of your money gets taken out of your account. You can keep track of how much money you have left on your phone by checking your 'balance'. If you run out of money, you won't be able to make any more calls or send messages, just like how you can't take any more money out of your piggy bank when it's empty.
Pay as you go phones are great because you only pay for what you use! So, if you don't use your phone too much, it can be less expensive than having a monthly bill.