To activate NVIDIA Highlights in Fortnite Battle Royale you’ll need to update to the Fortnite NVIDIA Highlights patch on January 10th, and have GeForce Experience 3.12 or higher, the Fortnite Game Ready driver, and a GeForce GTX graphics card.
Once everything’s ready, launch Fortnite, and select Battle Royale. GeForce Experience will ask if you want to enable NVIDIA Highlights for Fortnite Battle Royale. After you click "Yes", kill, death, and Victory Royale Highlights will automatically be recorded without any further input.
At the end of your match, select the “Highlights” button on your lower right. This will showcase the Highlights captured, and from this screen you can select which Highlights to save to your Gallery, and which to share immediately to Facebook or YouTube.