No problem. Hopefully you’ll get that all sorted! 
With the USD invoices, firstly you will need to enable multi-currency on your account, this can be done in the Account Settings >> All Settings >> Multi-currency settings:
Enable USD for your account, and that’s it - it’ll be enabled for sales and purchase invoices.
Then, when it comes to creating an invoice, you can change the currency on the right hand side:
Or if you wish to upload a CSV file, you can include a currency and exchange rate column as part of the details. There’s more information on uploading invoices, here.
There’s quite a bit to invoicing in multi-currency, but QuickFile will handle most of it for you. There’s a run down on it in our guide, including how to pay a foreign currency invoice from a GBP bank account.
I hope this helps, but please don’t hesitate to get in touch if you have more questions