If you are using Shippo's rates (USPS or DHL Express), you will be billed by Shippo for both the $0.05 label fee and the shipping rate. This is because you are essentially using Shippo's "account" with these carriers.
If you are using your own carrier account credentials (e.g. with FedEx, UPS), Shippo will only invoice you for the $0.05 label fee. Your carrier will bill you directly for the actual cost of shipping.
We charge our customers' credit cards when you've exceeded $100 in purchases, or when it's been over 7 days since your last invoice, except for your first bill. Your first invoice after you create your account will be charged once you've exceeded $25 in purchases.
If you have not yet been invoiced for a label, you'll find the charge under "Unbilled items" on your billing tab. To look at your invoices and see how much you'll be charged, you can check the Billing tab in your account.