The Rpi recognized it immediately on my system. This is a setup guide that details the steps to take to make sure it’s working: https://howchoo.com/networking/how-to-set-up-the-edimax-ew-7811un-usb-wifi-adapter-on-your-raspberry-pi
It assumes you know how to get to a command line interface as you will need to set it up as the primary. Also note that it is much better to disable the RPi4 wifi to use this.
This discussion (fgoldino comments) show you how to disable the onboard wifi: Support for USB network adaptors (Feature Unavailable) - #26 by rgoldino