How do I screen record on my iPhone 15?

Open the Control Center (swipe down from the upper right edge) and tap on the little "+" symbol in the upper left corner. Then tap Add a Control at the bottom, and select Screen Recording.

Back at the Control Center: when you tap on the Screen Recording icon, it will count down from 3 to give you time to get to where ever you want to record. To stop, there should be a red status bar, or dynamic island, or clock icon at the top of your screen to tap on. You can also go to the Control Center and tap the red Screen Recording icon. The video will be saved to your Photos.