A Charge Item is anything that you plan to charge money for. Think tuition, registration fee, deposit, book fees, t-shirts, late fee, etc.
Charge Items are essentially labels you'll pick from when configuring your program and class pricing. Keep in mind that you will be using these labels in your reporting.
Once you begin collecting payment from your customers, you will be able to pull up a report outlining which transactions are tied to which charge item, as well as the class and program name tied to this transaction.