How do you use an external hard drive with an Apple laptop?

If you are getting a "Silicon" 2020 model it has USB-C. You can buy a USB-A/B to USB-C adapter.

e.g. USB-C - USB adapter http://store.apple.com/us/product/MJ1M2AM/A/usb-c-to-usb-adapter

I should add you can get third party adapters with more ports but carefully check the speed specifications. I have one with 3 ports but only one does USB3, the others are USB2 and are designed for a mouse and another peripheral (e.g., an old flash drive)..