Cash accounting tracks the actual money coming in and out of your business.
In cash accounting, if you get an invoice for something, you don't record the cost in your books until you've paid the invoice. Similarly, when you send an invoice to a customer, you don't record the sale in your books until you receive the money from the customer.
For example, if you send an invoice on Tuesday, and don't receive the payment in your account until Thursday, you record the income against Thursday's date in your books.