The complete driver package is offered for download at the beginning of Bootcamp Assistant. There is a checkbox to be selected, which will cause a pause of a couple of hours (depeding on the speed of your network), during which the driver package is downloaded.
After Windows is installed in the Bootcamp partition, and booted up, you launch the driver package, which takes care for everything.
If you did forget to download the driver package, you can start over with BootCamp Assistant, or search in the Apple Support site for manual download. But this requires to select the correct driver package for your Bootcamp version and for your specific machine, something which Bootcamp Assistant does automatically for you.